2 1/2 cups unbleached all-purpose flour
1 tablespoon baking powder
1/2 teaspoon baking soda
1 teaspoon salt
2 tablespoons shortening
8 tablespoons unsalted butter (1 stick), sliced
2 tablespoons unsalted melted butter
1 cup cold buttermilk
Heat oven to 450 degrees. Whisk flour, baking powder, baking soda, and salt in large bowl.
Add shortening to flour mixture; break up chunks with fingertips until only small, pea-sized pieces remain.
Working in batches, drop butter slices into flour mixture and toss to coat
Pick up each slice of butter and press between floured fingertips into flat, nickel-sized pieces.
Repeat until all butter is incorporated; toss to combine. Freeze mixture (in bowl) until chilled, about 15 minutes.
Add all but 2 tablespoons of buttermilk to flour mixture; stir with fork until ball forms and no dry bits of flour are visible, adding remaining buttermilk as needed. Transfer dough onto center of prepared work surface, dust surface lightly with flour.
Bring dough together into cohesive ball.
Roll dough into 10-inch square about 1/2 inch thick
Cut out 3-inch rounds with floured biscuit cutter, dipping cutter back into flour after each cut.
Carefully transfer rounds to ungreased baking sheet, spaced 1 inch apart.
Brush biscuit tops with melted butter. Bake until tops are golden brown, 15 to 17 minutes.
Let cool on baking sheet 5 minutes before serving.