Mix egg and buttermilk together, set aside.
Combine flour, salt, and baking powder in a large mixing bowl. Add the butter and cream cheese to the bowl, and use your hands to coat each piece of butter and cream cheese with flour. Then begin pressing the butter and cream cheese between your fingers to flatten each piece. Instead of making pea shapes, make flat disks with the butter, cream cheese, and flour. Continue until the mixture looks scraggly.
Pour in the egg/buttermilk mixture. Mix with your hands to incorporate the ingredients. You will need to continuously rub your hands together to keep the sticky dough from accumulating on your hands. The dough will come together into a ball in a few minutes.
If the dough is sticky, shape the dough into a disk and wrap it tightly in plastic wrap. Let it chill in the fridge for about 30 minutes or until it is no longer sticky.
The dough rolls best when it is closer to room temperature, so if you store it in the fridge or freezer for an extended period of time, let it rest wrapped in plastic for an hour or two to bring it back to room temp before rolling.
Work the dough a little with your hands to soften it up and flatten it some. Dust gluten-free flour onto your work surface, rolling pin, and the dough to prevent sticking. Roll to approximately ⅛-inch thick. Transfer to a 9-inch deep-pie plate, trimming and shaping edges as you like.
Preheat the oven to 190°c.
