Heat the oven to 450°F.
Microwave the butter in an 8-inch square baking dish until melted.
Whisk the flour, sugar, baking powder, and salt together in a large mixing bowl.
Stir in 2/3 cup buttermilk; continue to add more buttermilk until a loose dough forms.
(I used about 2-3 Tbsp more than the 2/3 cup)
Dump the batter into the pan and use your fingers to gently press the dough out into an even layer.
Using a knife, cut the biscuits into 9-12 squares.
Bake for 12-15 minutes until golden.