Step 1

Preheat oven to 425°. Pulse baking powder, salt, sugar, baking soda, and 3½ cups flour in a food processor to combine. Add chilled butter and pulse until largest pieces of butter are the size of a pea. Transfer to a large bowl and gradually drizzle buttermilk over top, tossing with a fork as you go to incorporate. Knead mixture a few times in bowl until a shaggy dough forms (mixture will look a little dry), then turn out onto a clean surface and pat into a 1"-thick square.

Step 2

Using a knife or bench scraper, cut dough into 4 pieces. Stack pieces on top of one another, sandwiching any loose dry bits of dough between layers, and press down to flatten. Lift up dough with bench scraper and dust surface with flour. Roll dough into a 1"-thick rectangle and trim a thin border around sides of dough to create clean edges. Cut into a 4x3 grid to make 12 biscuits (don’t reroll scraps). Transfer to a parchment-lined baking sheet, spacing 2" apart; freeze 10 minutes.

Step 3

Brush tops of biscuits with melted butter and place in oven. Reduce oven temperature to 400° and bake biscuits until deep golden brown on bottom and golden on top, 20–25 minutes.

Step 4

Do Ahead: Biscuits (unbaked) can be made 1 month ahead. Freeze, uncovered, on baking sheet until solid, then transfer to a resealable plastic bag. Do not thaw before baking, but add a few minutes to baking time.