from America's Test Kitchen
2 cups (10 oz) unbleached all-purpose flour
1 Tbs double-acting baking powder
1 Tbs sugar
1 tsp salt
1/2 tsp baking soda
4 Tbs cold unsalted butter, cut into 1/4-inch cubes
1.5 cups cold buttermilk
To form and finish biscuits:
1 cup (5 oz.) unbleached all-purpose flour, distributed in rimmed baking sheet
2 Tbs unsalted butter, melted
Adjust oven rack to middle position and heat oven to 500 degrees.
In food processor, pulse flour, baking powder, sugar, salt, and baking soda to combine, about six 1-second pulses. Scatter butter cubes evenly over dry ingredients; pulse until mixture resembles pebbly, coarse cornmeal, eight to ten 1-second pulses. Transfer mixture to medium bowl. Add buttermilk to dry ingredients and stir with rubber spatula until just incorporated (dough will be very wet and slightly lumpy).
Spray 9-inch round cake pan with nonstick cooking spray; set aside. Generously spray inside and outside of 1/4 cup dry measure with nonstick cooking spray. Using 1/4 cup dry measure and working quickly, scoop level amount of dough; drop dough from measuring cup into flour on baking sheet (if dough sticks to cup, use small spoon to pull it free). Repeat with remaining dough, forming 12 evenly sized mounds.
Dust tops of each piece of dough with flour from baking sheet. With floured hands, gently pick up piece of dough and coat with flour; gently shape dough into rough ball, shake off excess flour, and place in prepared cake pan. Repeat with remaining dough, arranging 9 rounds around perimeter of cake pan and 3 in center. Brush rounds with hot melted butter, taking care not to flatten them.
Bake 5 minutes, then reduce oven temperature to 450 degrees; continue to bake until biscuits are deep golden brown, about 15 minutes longer.
Cool in pan 2 minutes, then invert biscuits from pan onto clean kitchen towel. Turn biscuits right side up and break apart. Cool 5 minutes longer and serve.