Combine gluten free flour, sugar, and salt in a bowl. Cut in the butter using a pastry cutter, fork, or simply your hands. Mix and crumble together until the mixture resembles coarse meal. Add ice water 1 tablespoon at a time, tossing and stirring with a fork until it just holds together. Wrap in plastic wrap and let rest in the fridge for at least 30 minutes.
To make the filling, whisk the sugar, tapioca flour, and cinnamon together, then add the black raspberries and vanilla and toss lightly to combine.
Preheat the oven to 400℉. Divide the ball of dough in half, and roll out 1 dough disk on a floured work surface to about an 11-inch round. Transfer to a 9-inch pie dish. Trim the excess dough, leaving a ¾-inch overhang.
Spoon the berry filling into the pie crust, and don't pour in the liquid at the bottom of the bowl.
Roll out the other dough disc and fit it onto the pie dish. Press the edges of the dough together, then crimp with a fork (trim any excess or sort of tuck and press to incorporate into the rest of the dough). Make four slivers in the center of the pie.
Place the pie on a baking sheet, place it in the oven, and bake in the middle of the oven for 25 minutes. Reduce the temperature to 350°F and bake the pie for 35-45 minutes more, or until the crust is golden and the filling is bubbly. Remove from the oven and cool on a rack until room temperature, at least two hours.
Notes
Tips
Use ap flour: Substitute 2 ½ cups of all purpose flour for the gluten free flour if needed.
Rest the dough - Pie dough needs at least 30 minutes to chill before it's rolled out, so don't skip this step. You can also make the crust in advance and keep it in the fridge for up to 3 days, or freeze it for up to 3 months. Defrost the crust in the fridge before using.
Do a crumble topping: Make half of the recipe for the pie crust, then do a simple crumble topping by whisking 1 cup flour with ½ cup sugar, then rub in ¼ cup of unsalted butter, and spread it evenly over the top of the pie.
Let the pie sit - It's equally important to let the pie sit after it's fully baked. I prefer to let the pie cool completely to room temperature, for at least 2 hours, to allow the filling to set. Let's avoid a watery pie filling!