Grind the cashew nuts in a food processor to fine powder. Combine with coconut flour and baking powder and mix. Set aside.
In a mixing bowl beat the egg whites until thick and foamy.
In another bowl beat together the eggs and erythritol for 3-4 minutes, until the mixture nearly triples its volume. Add vanilla and mix shortly to get absorbed. Gradually add the dry ingredients, folding them gently with a rubber spatula. Alternate with the yogurt as the mixture will become very thick.
At the end gently combine the egg whites with the cashew batter, mixing carefully with the spatula.
Divide the batter between two 7 inch/ 18 cm cake pans, greased and lined with circles of parchment paper.
Bake at 350°F/ 180°C for about 40 minutes or until a toothpick inserted in the batter comes out clean.
Remove the layers from the pans in 5-10 minutes and let them cool on a wire rack.
Combine flax seed meal and water. Mix very well and set aside for 5 minutes.
In a bowl combine coconut flour and baking powder. Mix very well and set aside.
In a large mixing bowl combine the soaked flax seeds, egg yolks and erythritol. Whisk very well until smooth. Add vanilla, yogurt and coconut oil and whisk again. Gradually add the dry ingredients, mixing gently with a rubber spatula.
Transfer the batter to a greased cake pan, lined with a circle of parchment paper.
Bake at 350°F/ 180°C for 40-50 minutes or until the top becomes golden brown and a toothpick inserted in the centre comes out clean.
Let the layers cool completely before assembling the cake.
In a large mixing bowl combine all ingredients. Whip them with an electric mixer until thick and fluffy: about 2 minutes.
Place one cashew layer on a serving plate. Generously spread from the mascarpone frosting on top (about ¼ of the whole quantity). Repeat the process with the coconut layer. Place the second cashew layer on top.
Frost all around with the remaining icing.
Decorate with fresh berries.
When you grind the cashew nuts, be careful not to process them for too long because you may end up with a cashew butter. You can also use ready-made cashew flour instead: same quantity.
For the cashew layers you need a sweetener with slightly crystalline structure. This is necessary to help the eggs increase their volume (like sugar). For the frosting it is better to use powdered sweetener as it melts easily when being mixed.
If you like your cake with lots of fruit, you can add berries also between the layers. Blueberries and raspberries are the best choice in this case.