Place the oven rack in the middle of the oven and preheat to 450F. Add the butter to a 9 x 9-inch casserole dish and place inside the oven while its preheating.
In a large bowl mix the flour, salt, baking powder and sugar. Add the buttermilk and stir until just combined.
Remove the casserole dish from the oven and pour the batter on top of the hot butter. Use a spatula or knife to spread the dough. Run the knife through the dough cutting 9, 3 inch squares.
Bake for 20-25 minutes rotating the pan once halfway through cooking until the tops of the biscuits are golden brown. Serve immediately.
