Preheat the oven to 175C/350F.
Line and grease a 20cm/8 inch round cake. A spring form tin is best as it will allow for easy serving at the end.
Place the egg whites into the clean bowl of a kitchen stand mixer fitted with a whisk attachment.
Whisk the egg whites on medium/high until soft peaks form.
Slowly add the maple syrup, 1 tablespoon at a time, until large peaks have formed,
Continue whisking on medium/high and add the vanilla extract.
Add the egg yolks, one at a time. Only add the next yolk when the previous one has been fully incorporated. Whilst still whisking, pour the milk into the egg mixture.
In a separate bowl, lightly whisk the coconut flour and baking powder together. Ensure that the coconut flour has no lumps in it.
Turn the whisk to low and add the flour mixture. (If you keep it on high then you will most likely end up wearing the flour). Once incorporated, return the whisk speed to medium/high to fully mix all the ingredients.
Pour the cake mixture into the prepared tin and bake for 14-16 minutes, or until cooked through.
Remove from oven and allow to cool in the tin.