Flaky Biscuits

From 6 Bittersweets
Adapted from Fine Cooking [Click on the link for helpful step-by-step photos!]

8 oz. (1 3/4 cups) unbleached all-purpose flour; more as needed for shaping the dough
1 Tbs. granulated sugar
2-1/4 tsp. baking powder
3/4 tsp. kosher salt
1/4 tsp. baking soda
4 oz. (8 Tbs.) very cold unsalted butter
3/4 cup very cold buttermilk
[I substituted 1/2 cup yogurt mixed with 1/4 cup milk]