Preheat the oven to 450°F (230°C) and line a baking sheet with parchment paper.
Mix dry ingredients: In a large bowl, whisk together flour, baking powder, salt, and sugar.
Cut in the butter: Use a pastry cutter or fork to blend cold butter into the flour mixture until it forms coarse crumbs.
Add buttermilk: Pour in the cold buttermilk and stir gently until the dough comes together. Do not overmix.
Shape the dough: Turn the dough out onto a lightly floured surface and gently pat it into a ¾-inch-thick rectangle. Fold once or twice for flaky layers, then cut out biscuits with a round cutter.
Bake: Place biscuits on the prepared baking sheet and bake for 10–12 minutes or until golden brown.
Brush and serve: Brush warm biscuits with melted butter and serve immediately.