Preheat your oven to 450°F (230°C).
Melt the butter in a microwave-safe bowl or saucepan. Pour it into an 8×8 or 9×9 inch baking dish.
In a large bowl, mix together the flour, baking powder, salt, and sugar.
Add the buttermilk to the dry ingredients and mix until just combined. The dough will be quite wet and sticky.
Pour the dough into the baking dish, directly on top of the melted butter. Spread it out evenly. The butter will rise up around the edges and over the top of the dough.
Using a knife, cut the dough into 9 squares before baking.
Bake in the preheated oven for about 20-25 minutes, or until the tops are golden brown.