Preheat oven to 425°F (220°C). Grease a 9x9 inch baking pan.
In a large mixing bowl, whisk together flour, sugar, baking powder, and salt.
Cut in the cold butter using a pastry cutter or fork until the mixture resembles coarse crumbs.
Pour in the buttermilk and stir until just combined. Do not overmix.
Transfer the dough to the greased pan and gently press it evenly into the pan.
Score the dough with a knife to make 9 squares (do not cut all the way through).
Bake for 20–25 minutes or until the top is golden brown.
If desired, brush the tops with melted butter after baking.
Let cool slightly before serving.