Keto lemon layer cake with lemon curd and mascarpone frosting

Keto lemon layer cake with lemon curd and mascarpone frosting

This cake is ‘extra’ as the young people say! Extra effort, extra time, and extra flavor — for an extra special occasion. Any low-carb foodie will appreciate the moist lightly lemon-flavored layers of cake, which holds the rich burst of lemon curd accompanied by a whipped mascarpone frosting. Tastes like spring!

Keto lemon layer cake with lemon curd and mascarpone frosting

This cake is ‘extra’ as the young people say! Extra effort, extra time, and extra flavor — for an extra special occasion. Any low-carb foodie will appreciate the moist lightly lemon-flavored layers of cake, which holds the rich burst of lemon curd accompanied by a whipped mascarpone frosting. Tastes like spring!
USMetric
20 servingservings

Ingredients

Lemon curd
  • 6 6 large egg yolklarge egg yolks
  • ½ cup 125 ml powdered erythritol
  • ½ cup 125 ml lemon juice
  • 1 tbsp 1 tbsp lemon zest, finely grated
  • 3 oz. 75 g unsalted butter, cubed
Lemon layer cake
  • 23 cup 150 ml (75 g) coconut flour
  • ½ cup 125 ml (50 g) oat fiber
  • ¼ cup 60 ml (25 g) whey protein isolate
  • 2 tsp 2 tsp (10 g) baking powder
  • ½ tsp ½ tsp salt
  • 8 oz. 225 g unsalted butter, softened
  • 23 cup 150 ml (110 g) granulated erythritol
  • 8 8 large egglarge eggs
  • 1 cup 225 ml heavy whipping cream
  • 2 tsp 2 tsp vanilla extract
  • 2 tbsp 2 tbsp lemon juice
  • 2 tbsp 2 tbsp lemon zest
  • 5-6 drops liquid sweetener, to taste
Mascarpone frosting
  • 2 cups 475 ml heavy whipping cream, chilled
  • 1 cup 225 ml powdered erythritol
  • 2 tsp 2 tsp vanilla extract
  • 16 oz. 450 g mascarpone cheese, chilled
  • 1 1 large lemon, finely grated zest

Instructions

Instructions are for 20 servings. Please modify as needed.

Lemon curd

  1. In a 2-quart saucepan over low heat, whisk together the egg yolks, sweetener, lemon juice, and lemon zest. Whisk constantly until the mixture reaches 170°F (75°C) on a candy thermometer and begins to thicken. If you don’t have a candy thermometer, you will know that the curd is thick enough when it coats the back of a spoon and begins to cling to the whisk. Remove from the heat.
  2. Add the butter, one cube at a time, whisking constantly to melt the butter and incorporate it into the lemon curd.
  3. When the butter is fully incorporated, strain the curd to remove any lumps or larger pieces of zest. Cover with plastic wrap, pushing the wrap gently onto the top of the curd to prevent a skin from forming.
  4. Let fully cool for at least an hour before assembling the cake.

Lemon layer cake

  1. Preheat the oven to 350ºF (175°C). Liberally grease two 8-inch round cake pans and line the pans with parchment paper.
  2. In a large bowl, whisk together the coconut flour, oat fiber, protein isolate, baking powder, and salt; set aside.
  3. In a separate large bowl, use a hand mixer or stand mixer to whip the butter and granulated sweetener. Add the whole eggs one at a time, beating well after each addition. Stir in the heavy cream, vanilla extract, lemon juice, lemon zest and liquid sweetener by hand. Add the dry ingredients and mix by hand until just incorporated.
  4. Divide the batter evenly between the prepared cake pans. Bake for 20 to 25 minutes, until a toothpick inserted in the middle of a cake comes out clean.
  5. Let the layers rest for about 10 minutes before removing from the pans to cooling racks to cool completely.

Whipped mascarpone frosting

  1. To make the frosting, start by whipping the cream with a hand mixer in a large mixing bowl.
  2. As you whip the cream, sprinkle in the sweetener and extract. When thickened, add the mascarpone and whip just until firm.
  3. Stir in the lemon zest by hand and refrigerate until ready to frost the cake. If you refrigerate for longer than 30 minutes, the frosting may become too firm to work with easily.

Assembling the cake

  1. To assemble, slice each cake round in half horizontally.
  2. Place one layer on a cake plate or cardboard round and spread 1/3 of the lemon curd on top. Use a light hand or a piping bag to cover the lemon curd with a thick layer of mascarpone frosting.
  3. Add another layer of cake followed by another 1/3 of the lemon curd and another thick layer of frosting. Repeat until the four layers of cake are assembled.
  4. Cover the top and sides of the assembled cake with the remaining frosting.
  5. Garnish with additional lemon zest if desired.
  6. Cover and refrigerate for at least 8 hours or overnight before serving.

Kristie's tip!

When zesting the lemons, be careful to include only the yellow zest; the white pith underneath is bitter-tasting and will affect the flavor of your curd.

You can make powdered sweetener by putting granulated sweetener in a clean, dry blender or coffee grinder. Measure after powdering the sweetener.

Storing the cake

If covered well, the cake will keep in the refrigerator for up to 5 days.

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30 comments

  1. Jordan
    Can the cake be frozen?
    Replies: #3, #5
  2. Kit Schroeder
    I can't wait to try this, looks DELISH!!! I do have a question about the lemon curd - Should it read to add 1/3rd of the lemon cream curd to each layer? It says add half, but there are four layers.
    Reply: #4
  3. Kristin Parker Team Diet Doctor

    Can the cake be frozen?

    Yes, you may wish to slice it and then freeze the individual portions.

  4. Kristie Sullivan, PhD Team Diet Doctor
    Yes, I’ve just realized that I need to fix that! Thanks!
    Reply: #9
  5. Kristie Sullivan, PhD Team Diet Doctor
    I’ve frozen the cake layers, but I’m not sure how the whipped mascarpone would hold up to freezing.
  6. Tammy Milburn
    I have two questions -
    (1) under Kristie's tips, it says to reserve the egg whites for the cake layers, but the recipe calls for 8 whole eggs. Is that a typo?
    (2) should the bake time be adjusted if using 4 of the 8" layer pans?
  7. Simon
    Thank you so much for adding metric grams. So accurate and easy, especially with add on scales.
  8. Linda
    I only made the mascarpone frosting and put it into glass jars to serve as I am currently trying the relaxed carnivore diet but wanted a "dessert". It's lovely to eat with a spoon 😋
    I made the amount of the frosting for 5 servings of cake and split that in two for me and hubby.
    So I rated it 5 stars but have only tried and tested the frosting... No fault with that!! 😁
  9. Kit
    If I made it as a regular two layer cake, I could just keep it as is. This looks so good!
  10. Sandra
    What is oat fibre.
    Reply: #11
  11. Kristin Parker Team Diet Doctor

    What is oat fibre.

    Oat fiber is the insoluble outer husk, not part of the oat itself. You may be able to get it from Amazon or iHerb.com

  12. Mariana Rodica
    si se puede, que pongáis esta receta en la pagina española .....
  13. Vanessa McAfee
    I don't have oat fibre, what can it be substituted with? I have xanthum gum and psyllium husk, could I use this?
    Reply: #14
  14. Kristin Parker Team Diet Doctor

    I don't have oat fibre, what can it be substituted with? I have xanthum gum and psyllium husk, could I use this?

    Unfortunately there is not a good substitution for oat fiber.

  15. Tammy
    Another masterpiece by Kristie - thanks for a perfect Easter dessert !
  16. Mary
    This cake takes time, as all good cakes do. I found all of the ingredients but had to really search for the oat fibre.
    I found it difficult to get the eggs and butter incorporated properly. Took a lot of mixing and I ended up switching to the whip attachment for my kitchen aid to get a good consistency before adding the dry ingredients. After baking, the pans were quite buttery on the bottoms and the cakes did not rise well. Most likely due to lack of mixing the dry ingredients well enough. When I try this cake again, I will do a better job of whisking the dry ingredients and make sure that my butter is just a bit softer before starting. The cakes were difficult to slice since mine hadn't risen well but i made it work. The crumb of the cake is course, similar to a sponge type cake, but delicious just the same. I'm sure it will be better next time with the changes I intend to make! I've made lemon curd plenty of times before, never had one turn our quite this dark yellow but it tasted delicious and you'd never know that it is sugar free. The "frosting" was easy to make although where I live, expensive. I'm serving the cake for Easter Dinner tomorrow and looking forward to my family's comments. I think they will be pleasantly surprised that mom's weird keto dessert will taste so good!
    The left over egg whites were used to make keto bread.
  17. Jenny
    I made this cake because it looked so good to only be 3 grams a serving. Also, for Easter, as my sister and I are doing Keto. I had to make another cake (Blum's Coffee Crunch Cake - also a time taker as you make honeycomb to cover the whipped cream frosting - this is a favorite of my family - surprisingly, I did not have a problem NOT eating it). Back to the Lemon Cake - problems I had:
    I could not find Oat Fiber in time to make this, so I substituted oat bran, which didn't seem to hurt anything. The cake does not rise as well as a "normal" cake, but it was still fine. The lemon curd: I had problems with this - it basically oozed out of the layers as it didn't thicken enough, in spite of my best efforts. Had I known it wouldn't hold up on the cake, I would have added Xanthum gum to thicken before putting on the cake. The frosting is to die for, so good. However, next morning, belly not too happy. Probably too much erythritol, overall, for my digestive track (between cake and curd and frosting). I will probably have to throw out what has not been consumed, as I had this problem two days in a row, even with 1/20th serving of the cake (very thin slice).
    Reply: #19
  18. Debbie
    We had this for Easter and no one would have known it was low carb. It was wonderful. Want to try to convert it to chocolate. mmmmm
  19. Kristin Parker Team Diet Doctor

    However, next morning, belly not too happy. Probably too much erythritol, overall, for my digestive track (between cake and curd and frosting). I will probably have to throw out what has not been consumed, as I had this problem two days in a row, even with 1/20th serving of the cake (very thin slice).

    Unfortunately, that may have been the oat bran. Oat bran is not a good keto substitute for oat fiber. Oat fiber is the completely insoluble outer husk, not part of the oat itself.

  20. Christy
    I'm thinking of making this into a poke cake, pouring the lemon curd over the poked cake then frosting with the mascarpone. Any idea how long I should cook it in a 9x13 glass pan? Thanks!
    Reply: #21
  21. Kristin Parker Team Diet Doctor

    I'm thinking of making this into a poke cake, pouring the lemon curd over the poked cake then frosting with the mascarpone. Any idea how long I should cook it in a 9x13 glass pan? Thanks!

    I am not sure, we have not tested this in a larger pan.

  22. Arlene
    Kristin, can I substitute cream cheese for half of the mascarpone?
    Reply: #23
  23. Kristin Parker Team Diet Doctor

    Kristin, can I substitute cream cheese for half of the mascarpone?

    We have not tested this with cream cheese and mascarpone. They have different consistency and taste.

    Reply: #24
  24. Arlene
    I did the 8 oz of cream cheese and 8 oz marscapone it turned out fine.
  25. marlene
    I am planning on making this... It looks soooooo ooooo oooo good. I am the only one in my family of 4 (2 are an 8 and 6 yr old and will eat pretty much whatever I make) doing keto and want some yummy "treats" for them.
  26. Filter for no sweeteners in search bars please
    Can this site add a filter to the searches that discards recipes with sweeteners? It's getting really annoying seeing recipes with sweeteners.

    Not only is it still not consistent if they cause you to jump out of ketosis or not (it seems to have done that on one test Endfeldt did, but that's a anecdote). They are also fairly expensive.

    Reply: #27
  27. Kristin Parker Team Diet Doctor

    Can this site add a filter to the searches that discards recipes with sweeteners? It's getting really annoying seeing recipes with sweeteners.
    Not only is it still not consistent if they cause you to jump out of ketosis or not (it seems to have done that on one test Endfeldt did, but that's a anecdote). They are also fairly expensive.

    Avoiding desserts is one easy way to accomplish this! Our recipe filters can select main or side dishes and you can avoid desserts.

  28. Emily
    I made this last night, and it’s fabulous. Probably the best keto dessert I have ever made. Non-keto people said they would have had no idea this was low-carb if I didn’t tell them The texture was very cake-like. In my oven, using silicone pans, it took 30 minutes to bake. The brand of oat fiber really affects the taste. I like Lifesource. I threw away the oat fiber I had from Honeyville, as it does not taste good. I use Sukrin Melis and Sukrin:1 in place of the straight erythritol called for in the recipe. I did not slice the cake layers, just put all the lemon curd in between the two layers, then frosted the cake with the mascarpone frosting, so I have leftover frosting in the fridge. That frosting is so good! Thank you, Kristie!
  29. Frieda Rossouw
    Thank you, Kristine! This is a awesome cake, it is delicious. With this cake and icing there is hope for my daughter to have a cake in the form of a princess dress cake for her birthday.
  30. Sherry Harrold
    I just made this cake. The lemon curd was delicious, frosting was to die for..l have got several ideas for that in other recipes. The cake as good but it didn’t stay together when I sliced it so the tops were broke all to pieces..any suggestions..next time I probably want cut them in two.

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