Preheat the oven to 200C/400F degrees.
Grease a square baking tin and line with parchment paper.
In a bowl, beat the butter and erythritol together until combined.
Add the egg yolks, vanilla extract and coconut milk and cream. Mix thoroughly.
Add the coconut flour, salt and baking powder. Stir well.
In a separate bowl, whisk the egg whites until stiff.
Gently fold the egg whites into the cake batter.
Pour into the cake tin and bake for 20 minutes until golden and firm.
Remove from the oven and allow to cool.