Chef John's Buttermilk Biscuits

Ingredients (7)

• ✓ 2 cups all-purpose flour
• + 2 teaspoons baking powder add to pantry
• + 1 teaspoon salt add to pantry
• ✓ ¼ teaspoon baking soda
• + 7 tablespoons unsalted butter, chilled in freezer and cut into thin slices add to pantry
• ✓ ¾ cup cold buttermilk
• + 2 tablespoons buttermilk for brushing add to pantry