Prepare the Batter. Preheat your oven and generously grease a donut pan. In a medium bowl, whisk together almond flour, coconut flour, sweetener, and baking powder. In another bowl, mix the eggs, melted butter, almond milk, and vanilla extract until smooth.
Combine and Fill. Add the wet ingredients to the dry ingredients and stir until a thick, smooth batter forms. Transfer the batter to a piping bag or zip-top bag with the corner cut off and pipe evenly into the donut pan.
Bake and Cool. Bake at 350F for 12-14 minutes until the donuts are set and lightly golden. Remove from the oven and allow them to cool in the pan before transferring to a wire rack. Keto donuts firm up as they cool, so patience pays off here.