In a microwave-safe bowl (or you can use the baking dish that you'll be baking these in if it's microwave-safe), melt stick of butter in the microwave.
Put melted butter into an 8x8 baking dish.
In a medium bowl, mix together the flour, sugar, baking powder and salt.
Pour in the buttermilk. Stir until a loose dough forms. Batter will be a bit sticky.
Pour biscuit dough into baking dish (right on top of the melted butter.) Some of the butter will run over the top of the dough, that's perfectly okay.
Cut the dough into 9 squares. This will help with cutting later when they are done too.
Bake for about 20-25 minutes, rotating dish once during baking.
Oven times do vary since different ovens have different hot spots, but basically biscuits should be golden brown on top and spring back to the touch.
If using unsalted butter, be sure to add 1 teaspoon of salt.
Eat within two days. Make sure to cover leftovers. If stored in the refrigerator, they will last for a week. These biscuits can also be frozen. Wrap well in freezer-safe plastic wrap and then store in a freezer-safe bag or container. Will freeze for up to 3 months.