In a mixing bowl, combine the almond flour, coconut flour, baking powder, and xanthan gum. Mix well. Chop the cold butter into small cubes.

In a high-speed blender or food processor, blend the dry ingredients and butter until a fine, crumbly texture forms.

Form the dough into two smooth balls and wrap them completely in plastic wrap. Refrigerate the dough for at least two hours.

Preheat your oven to 350F. Grease a 9-inch pie dish and set it aside.

In a small saucepan, add the blueberries, sweetener, lemon juice, and chia seeds. Place over low heat. Once it begins to simmer, stir gently for 4-5 minutes, then remove from heat.

Place each ball of dough between two pieces of parchment paper and roll them out. Make one piece larger than the other. Place the larger piece into the pie dish, allowing the sides to overhang. Fill with the blueberry mixture and spread it evenly. Top with the second layer of dough and crimp the edges. Brush with the whisked egg.

Bake the pie for 45-50 minutes, or until the top is golden brown. Remove from the oven and let it cool for a few minutes before serving.