Add the flour, baking powder, salt, and powdered sugar into a food processor. Cut the cold butter into cubes, then add it into the food processor.
Pulse the mixture a few times until the butter is broken up into smaller chunks.
Add the egg yolk and sour cream into the food processor, and blend until the ingredients become one cohesive dough.
Remove the dough from the food processor, form it into a ball, and transfer it to a floured work surface.
Sprinkle flour on top of the dough ball, then roll it out into a 9" circle. If the dough starts sticking to the rolling pin, add more flour to the top of the dough.
Butter an 8" tart pan or a shallow 8" pie dish. Transfer the dough to the tart pan and crimp the edges.
Poke holes in the bottom of the crust with a fork, then transfer the crust to the freezer and let it chill for 15 minutes. In the meantime, preheat the oven to 375℉ / 190℃.
Once the crust has chilled, crumple up a piece of parchment paper and gently lay it on top of the pie crust. Fill the parchment with rice or pie weights, gently pressing it into the crimps on the crust as needed.
Bake the crust for 10-15 minutes, until it starts to turn golden brown. Once the crust is done baking, reduce the temperature to 350℉ / 175℃.