Preheat your oven to 450°F . Place ½ cup (1 stick) of unsalted butter directly into an 8x8-inch baking dish. Put the dish in the oven while it preheats. After 5 to 8 minutes, the butter will be fully melted.
½ cup unsalted butter
While the butter melts, whisk together the flour, baking powder, salt, and sugar in a large bowl until evenly combined.
2½ cups all-purpose flour, 4 teaspoons baking powder, 1½ teaspoons salt, 4 teaspoons granulated sugar
Pour the buttermilk into the center of the dry ingredients. Gently stir and fold with a spatula until just combined and no dry flour is visible. The batter should be thick and wet like thick pancake batter, not a stiff dough. Do not overmix.
1¾ cups buttermilk
Carefully remove the hot dish from the oven and set it on a rimmed baking sheet. Pour the batter directly on top of the melted butter. Using a greased spatula, gently spread the batter until it reaches all four sides.
Grease a sharp knife and score the batter into 9 equal squares in a 3x3 pattern (do not cut all the way through). Bake at 450°F for 20 to 25 minutes until golden brown, puffy, and the edges are crispy and caramelized.
Let the biscuits rest in the pan for 5 minutes. Break or cut along the score lines into 9 squares. Serve warm with jam, honey, gravy, or butter.