Combine the spelt flour, salt, and baking powder in a resealable plastic bag. Place the bag in the freezer for 30 minutes.
Cube the butter and divide it into two portions: 2/3 of the butter and 1/3 of the butter. Refrigerate the 2/3 portion and freeze the 1/3 portion.
Transfer the cold flour mixture from the bag into a food processor using the standard blade (the S-shpaed blade). Pulse for a few seconds to combine to ensure that the salt and baking powder are fully distributed throughout the flour. (You can also do this by hand using a whisk.)
Add the refrigerated butter (2/3 portion) to the food processor. Pulse until the mixture resembles coarse sand. (You can also do this by hand using a pastry cutter or two knives.)
Add the frozen butter (1/3 portion) and pulse a few times until the butter pieces are pea-sized and evenly distributed. (You can also do this by hand using a pastry cutter or two knives.)
Add 1 1/2 teaspoons of ice-cold water and 1 teaspoon of apple cider vinegar to the flour butter mixture. Pulse a few times or gently incorporate using a wooden spoon or baking spatula.
Check the mixture by pinching it between your fingers. If it holds together, it’s ready. If it’s too dry, add ice-cold water 1/2 teaspoon at a time, pulsing between additions, until the mixture holds together.
Transfer the mixture back into the plastic bag. Knead gently from the outside of the bag until the dough comes together into a disk.
Refrigerate the disk for a minimum of 45 minutes.
Remove the dough from the refrigerator and place it on a floured surface. Flour the top of the dough and flour your rolling pin. Alternatively, you can place the floured dough between two pieces of parchment paper, or simply cover your floured dough with a sheet of plastic wrap. (See Video.)
Roll the dough into a 12-inch circle.
Place the rolled-out dough into a pie plate. Pie plates ranging in size from 8 1/2 to 10 inches will work. I used a 9 1/2-inch pie plate. Press the dough gently into the pan and crimp the edges as desired.
Refrigerate the prepared pie plate for at least 1 hour or up to 24 hours.
Use this single pie crust as directed in your recipe. Follow specific instructions for a par-baked (partially baked) pie crust, or blind baked (fully baked) pie crust, depending on your recipe.