Preheat your oven to 450 degrees Fahrenheit and place your 9x13 baking pan inside to preheat.

In a large bowl, whisk together 2 1/2 cups all-purpose flour, 1 tablespoon baking powder, 1/2 teaspoon salt, and 1 teaspoon sugar.

Add 6 tablespoons of cold, cubed unsalted butter to the flour mixture and work it in until the mixture resembles coarse crumbs.

Pour in 1 cup of buttermilk and 2 tablespoons of whole milk, then fold everything together until a shaggy dough forms.

Lightly flour a clean work surface and gently press the dough into a 3/4-inch thick rectangle.

Using a 2-inch biscuit cutter or the rim of a glass, cut out 12 biscuits and place them aside.

Carefully remove the hot preheated pan from the oven and pour 6 tablespoons of melted butter evenly across the bottom.

Place all 12 biscuits cut-side down into the hot butter, arranging them in 3 rows of 4.

Bake for 13 to 15 minutes, until the tops are light golden brown and the bottoms are deep golden.