Preheat your oven to 450°F (230°C).
In a large bowl, whisk together flour, baking powder, baking soda, and salt.
Cut in the cold butter using a pastry cutter or your hands until the mixture resembles coarse crumbs.
Make a well in the center and pour in the cold buttermilk. Stir gently until a dough forms. Add a splash more buttermilk if too dry.
Turn the dough onto a floured surface. Gently knead 2-3 times, then pat it into a ¾-inch thick rectangle.
Fold the dough over itself 2-3 times for flakiness, then pat it back down and cut out biscuits using a 2½-inch cutter.
Place biscuits on a parchment-lined baking sheet so they just touch. Bake for 12-15 minutes or until golden brown.
Brush with melted butter and serve warm.