Add flour, baking powder, sugar and salt to a food processor and process for 10 seconds until combined well. Add butter cubes and process until combined. Transfer mixture to a mixing bowl.
Add 1-1/4 cups buttermilk and carefully stir the mixture until dough forms. Using your hands, knead the mixture into a ball.
Turn the dough onto a lightly floured surface and using a rolling pin, roll the dough int a rectangle. Fold the dough into a letter shape and repeat, rolling into a rectangle. Fold into another letter shape and cover with plastic wrap. Refrigerate for 5 minutes.
Preheat oven to 425 and line a baking sheet with parchment paper. Remove dough from refrigerator and discard plastic wrap. Use a rolling pin to roll dough into 3/4" thickness.
Using a 3-4" round cutter, cut dough into rounds and place onto the prepared baking sheet. Fold remaining dough scraps together and roll again to 3/4" and cut additional biscuits until all of the dough is used.
Use remaining 1 tablespoon buttermilk to lightly brush the tops of each biscuit. Bake for 15-17 minutes until lightly browned on the top.