Step 1

Adjust oven rack to lower-middle position and preheat to 400°F. Should your kitchen be warmer than 75°F, please see our guide to baking in a hot kitchen before getting started; the specifics are focused on pie dough, but the overall principles are true of biscuits as well.

Step 2

Sift flour, baking powder, baking soda, and salt into a medium bowl, then whisk until well combined (this may take up to 1 minute). Add the butter, toss to break up the pieces, and smash each cube flat. Continue smashing and rubbing until the butter has mostly disappeared into a floury mix, although a few larger, Cheerio-sized pieces may remain. This can also be done with 4 or 5 pulses in a food processor, just take care not to overdo it. The prepared mix can be refrigerated up to 3 weeks in an airtight container, then used as directed below.

Step 3

Mash the sweet potato purée and milk together with a fork, or combine with an immersion blender until perfectly smooth. Add to the dry mix in a large bowl, and fold with a flexible spatula until fully absorbed. The dough will seem rather crumbly and dry at first, but keep mixing until it finally comes together. Once the dough forms a rough ball, turn out onto a lightly floured surface.

Step 4

With your bare hands, gently pat the dough into a squarish shape about 1/2-inch thick, then fold in half; repeat twice more for a total of 3 folds, using only enough flour to keep your hands from sticking. Finish by patting the dough to a thickness of 3/4 inch. If needed, dust away any excess flour, then cut into 1 3/4-inch rounds and arrange in a 10-inch cast iron skillet. Gather scraps into a ball, pat and fold a single time, then cut as many more biscuits as you can. The final round of scraps can be gathered and shaped into a single biscuit by hand.

Step 5

Bake until the biscuits are well-risen and golden brown, about 25 minutes (or longer if cut thicker than 3/4-inch). Let the biscuits cool about 5 minutes to help set their crumb, then serve as desired, whether alongside soups and stews or split for shortcake or breakfast sandwiches. Leftovers can be stored up to a week in an airtight container; to serve, split the stale biscuits in half, brush with melted butter, arrange on a baking sheet, and broil until golden brown, then serve with jam.