Preheat the oven to 450°F (230°C).
Place the butter in a cast iron skillet or an 8x8-inch baking dish and melt it in the preheated oven. Be careful not to let it burn.
In a separate bowl, whisk together the all-purpose flour, baking powder, granulated sugar, and salt. Stir in the buttermilk until just combined.
Remove the skillet or baking dish from the oven with the melted butter and pour the biscuit batter over the melted butter.
Bake for 25-30 minutes or until the biscuits are golden brown and set.
Cut the biscuits with a bench scraper or sharp knife. Let them sit in the pan for about 15 minutes to absorb the butter before serving.