In a large mixing bowl or food processor, combine the gluten free all-purpose flour blend, almond flour, sugar, and salt. Pulse or whisk to combine thoroughly.
Add the cold, cubed butter. Using a pastry cutter or food processor, work the butter into the flour until the mixture resembles coarse crumbs with pea-sized pieces of butter remaining.
In a small bowl, lightly beat the egg with 2 tablespoons of ice-cold water. Add this to the flour mixture and stir gently.
Add additional cold water, 1 tablespoon at a time, until the dough just comes together when pressed. It should be slightly tacky but not sticky.
Divide the dough into two portions (one slightly larger for the bottom crust). Shape each into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes.