Preheat your oven to 450°F (232°C).
Pour the melted butter into an 8×8-inch baking dish, making sure it covers the bottom evenly.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.
Gradually pour in the cold buttermilk, stirring just until combined. The dough will be sticky and slightly lumpy.
Transfer the dough into the prepared baking dish, directly over the melted butter. Use a spatula to spread the dough evenly.
Using a knife, gently cut the dough into 9 squares (3 cuts vertically and 3 cuts horizontally). This will allow the butter to seep into the cuts while baking.
Bake for 20-25 minutes or until the top is golden brown and the edges are crispy.
Remove from the oven and let the biscuits cool for 5 minutes before serving.