Flaky Sourdough Biscuits

Name: Flaky Sourdough Biscuits
Prep time: 20 min
Cook time: 12 min
Total time: 32 min
Cuisine: American
Ingredients: 2 cups (10 oz, 280g) all purpose flour; 2 cups (8.5 oz 240g) cake flour; 1 tablespoon + 1 teaspoon baking powder; 1 teaspoon baking soda; 1 tablespoon granulated sugar; 1 teaspoon table salt; 8 oz (2 sticks, 224g) unsalted butter, cold and cut into 16 pieces; 1 cup (8oz, 224g) unfed sourdough starter (100% hydration) at room temperature; 1 cup (8oz, 240ml) room temperature buttermilk, plus more for brushing