Preheat the oven to 170°C (338°F).
Mix almond flour, coconut flour, and baking powder in a bowl.
Separately mix eggs, erythritol, butter, and vanilla extract.
Combine the dry ingredients and the wet ingredients to make the batter.
Pour the batter into a cake mold.
Bake in the oven at 170°C (338°F) for 25 minutes.
Let it cool before serving.