Preheat the oven to 350°F. Grease the bottom and sides of a 9-inch tart pan with coconut oil and place a piece of parchment paper on the bottom of the pan.
Using a hand or electrical mixer, cream the butter and sugar together.
Stir in the apple cider vinegar and yolk of the egg (reserve the egg white).
In a separate bowl, mix together the almond flour, arrowroot powder and salt, then using a rubber spatula gently mix with the creamed butter mixture.
Beat the reserved egg white with an electrical mixer until stiff peeks form, then gently fold it into the batter.
Freeze batter for 10 minutes, then press it onto the bottom and sides of the pan.
Bake for 15 minutes or until the crust starts to turn brown.
Butter: substitute butter for ghee or palm shortening.Baking: You can keep your crust dough in the fridge and bake it when you're ready to make your pie or you can pre-bake it and store it in the fridge.