Step 1

Adjust an oven rack to the middle position and preheat the oven to 425°F. Whisk together the buttermilk and sour cream in a small bowl.

Step 2

In the bowl of a food processor, combine the flour, baking powder, baking soda, and salt and process until blended, about 2 seconds. Scatter the cold butter evenly over the flour and pulse until the mixture resembles coarse meal and the largest butter pieces are about 1/4 inch at their widest. Transfer to a large bowl.

Step 3

Add the buttermilk mixture to the flour mixture and fold with a rubber spatula until just combined. Transfer the dough to a floured work surface and knead until it just comes together, adding extra flour as necessary.

Step 4

With a rolling pin, roll the dough into a 12-inch square. Using a bench scraper, fold the right third of the dough over the center, then fold the left third over so you end up with a 12-by-4-inch rectangle. Fold the top third down over the center, then fold the bottom third up so the whole thing is reduced to a 4-inch square. Press the square down and roll it out again into a 12-inch square. Repeat the folding process once more. (See note for Cheddar Cheese and Scallion variation.)

Step 5

Roll the dough again into a 12-inch square. Cut six 4-inch rounds out of the dough with a floured biscuit cutter. Transfer the rounds to a parchment-lined baking sheet, spacing them about 1 inch apart. Form the dough scraps into a ball and knead gently 2 or 3 times, until smooth. Roll the dough out until it’s large enough to cut out 2 more 4-inch rounds, and transfer to the baking sheet.

Step 6

Brush the tops of the biscuits with the melted butter and bake until golden brown and well risen, about 15 minutes, rotating the pan halfway through. Allow to cool for 5 minutes and serve.