Before you start, make sure ALL the ingredients are at room temperature including eggs, lemon juice, unsweetened almond milk, and flours.
Preheat oven to 180°C (350°F).
Grease two 9-inch round cake pans with coconut oil or butter. Set aside.
In a large mixing bowl, combine almond flour, coconut flour baking powder, and baking soda. Set aside.
In another mixing bowl, add eggs (at room temperature) with sugar-free crystal sweetener. Beat on high speed for 45 seconds until foamy and lighter in color.
Bring back the mixing bowl with the dry ingredients. Make a well in the center of the flour and add the lemon zest, lemon juice, melted coconut oil, vanilla, and beaten eggs.
Beat gently on low speed to incorporate all the ingredients together and form a consistent cake batter.
Stop the electric beater, and using a spatula, fold in the blueberries into the batter.
Transfer half of the cake batter into one cake pan and the other half of the batter into the second cake pan. You now have two cake pans filled with roughly the same amount of cake batter.
Bake each cake layer for 20-25 minutes or until a skewer inserted in the center of the cake comes out clean. If you have a convection mode on your oven you can easily bake the two cake layers at the same time. Otherwise, it is preferable to bake one cake layer at a time. You can keep the second layer at room temperature while the first cake layer is baking.
Let the cake cool down for 10 minutes in the pan then release it on a cooling rack.
Cool down for at least 3 hours or until the cakes are at room temperature before frosting. Don't cool down in the fridge, or the cakes will lose their moisture and become dense.
Keto lemon buttercream
In a medium-size mixing bowl, add the soft butter, and using an electric beater, beat soft butter for 1 minute. Stop beater, then add softened cream cheese.
Beat on medium speed for about 1-2 minutes or until fluffy and light in color.
Stop the beater and add in lemon juice, unsweetened almond milk, and powdered sugar-free sweeteners.
Beat again, at low speed first, to prevent the powdered sugar from bursting outside of the mixing bowl, then on medium speed until the frosting is thick.
Use the frosting to assemble the 2-layer cake.
You can make the frosting ahead of time and store it in the fridge in an airtight container while the cake layers are cooling down.
Blueberry chia coulis
In a small saucepan, add blueberries, lemon juice, chia seeds, and sugar-free powdered sweetener.
Bring to a boil, smash the blueberries with a fork, then simmer 2-3 minutes, stirring constantly until it forms a slightly thick coulis.
Use the coulis between the cake layer, preferably add on top of the first layer of buttercream.
Store leftover frosting, coulis in an airtight container in the fridge for up to 3 days.
Store the lemon cake in the fridge in a cake box for up to 3 days. You can freeze the cake too, but I recommend freezing unfrosted cake for better taste when defrosted.