In a bowl combine the almond flour, coconut flour and baking powder. Beat the eggs and sweetener. Add the vanilla extract, milk and melted butter and beat until combined.
Sprinkle with a layer of the brown sugar and cinnamon mixture. Repeat with remaining batter and cinnamon-sugar mixture. To make the crumble, in a bowl combine all the ingredients. Sprinkle the muffins with crumb topping.