Preheat oven to 450°F and lightly grease a baking dish.
Melt butter and pour it into the baking dish.
Mix flour, sugar, baking powder, and salt until combined.
Add buttermilk and stir into a thick, sticky batter, adding more if needed.
Spread the dough evenly over the melted butter.
Cut the dough into 9 squares.
Bake for 25 to 30 minutes, rotating once, until golden brown.
Check doneness with a toothpick; it should come out clean.