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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15 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 !

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