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 into a mixing bowl.
Add 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 circle cookie cutter to cut dough into rounds, dipping into flour between cuts and twisting so it is done quickly. Place onto the prepared baking sheet with 1.5" in between them. Fold remaining dough scraps together and roll again to 3/4" and cut additional biscuits until all of the dough is used.
Use 1 additional tablespoon of buttermilk to lightly brush the tops of each biscuit. Bake for 15-17 minutes or until just golden brown and middles are cooked thru, no longer.
Remove and brush melted butter on top of each one, serve.