Mildly Sweet Sweet-Potato Biscuits

"Sweet potato adds flavor and sweetness—but not too much sweetness—to these moist biscuits. [Photographs: Marissa Sertich] Sweet potatoes started out as a way of stretching expensive refined flour in biscuit doughs for those who couldn't afford otherwise, but they're not just an economical step: They create moist, flavorful biscuits that are even more likely to be tender, because some of that sweet potato replaces what would otherwise be wheat gluten. Here are the steps to make them. Why this recipe works: * The moisture-absorbing nature of sweet-potato starch gives structure to the biscuits, while the starch that's broken down during the cooking process contributes a rich flavor and mild notes of sweetness. * Mashing the sweet potato by hand gives the biscuit lots of texture and preserves small pieces of sweet potato that offer little bursts of pure sweet-potato flavor...."