Heat oven to 425°F (220°C). Pulse the flour, baking powder, baking soda, salt, and sugar in a food processor to combine. Add the cold butter and pulse until pea-sized pieces remain.

Transfer to a bowl, add the sour cream and 2 tbsp milk, and stir with a fork until a shaggy dough forms.

Turn onto a floured surface, pat into a 3/4-inch rectangle, fold in half, and pat again. Cut with a floured 2-inch cutter without twisting.

Place biscuits on a parchment-lined sheet with sides touching, brush tops with milk, and bake 12 to 15 minutes until golden. Serve warm.