Preheat the oven to 425℉ and move a rack to the upper third of the oven. Line a baking sheet with parchment paper.
In a medium bowl, combine the flour, baking powder, sugar and salt. Work the butter into the flour mixture using a stand mixer (or your hands); your goal is an evenly crumbled mixture.
Drizzle a small amount of milk evenly over the flour mixture. Mix quickly and gently for about 15 seconds, until you have a cohesive dough. If the mixture seems dry and won't come together, add more milk a little at a time.
Place the dough on a lightly floured work surface. Shape it into a rough rectangle about ¾-inch thick. Fold it into thirds like a letter and roll gently with a floured rolling pin until the dough is ¾-inch thick again. Cut the dough into 2-inch squares with a sharp knife. Place the biscuits bottom-side-up on your prepared baking sheet. Brush the biscuits with milk to enhance the browning.
Bake for 15 to 20 minutes, until lightly browned. Remove them from the oven and serve warm.