Heat oven to 350F and prepare a 9×9 inch pan with non-stick cooking spray. In a large mixing bowl combine the almond flour, coconut flour, sweetener, and lemon zest, then stir until all ingredients are uniformly mixed.

Cut the softened butter into the flour mix with a fork. You may want to dig in with your hands to thoroughly incorporate the butter into the flour.

Press the dough into the prepared baking dish and bake for 15 minutes or until crust is golden. Set aside while you prepare the filling.

Bring a saucepan to medium heat and add butter, erythritol, and milk. Stir until the butter and sugar have completely dissolved.

Pour in lemon juice. Be sure to use a strainer if you are using freshly squeezed juice!

Slowly whisk in the eggs and stir continuously over medium-low heat until the mixture begins to thicken. This should talk about 5 to 10 minutes.

Transfer the lemon filling to your crust and return to the oven for 15 minutes. Prepare the topping.

In a small food processor or blender pulse the toasted coconut, almond flour, and butter until you have a grainy mixture.

Sprinkle topping on your lemon squares and return to the hot oven to crisp the top for approximately 5 minutes, or 1 minute under a hot broiler. Be careful not to burn the crumble!

Let cool before serving.