Place sweet potatoes in a large saucepan and cover with water. Bring to a boil and cook until fork-tender, about 15 minutes. Drain well, then puree in a food processor. Measure out 1 1/2 cups puree (discard any leftover or save for a different use). Place the puree in a small bowl, cover and chill in the refrigerator until chilled. (See notes)
1 large or 2 medium sweet potatoes
Place an oven rack on the lower shelf and preheat to 425°F. Line a large baking sheet (or 2 standard baking sheets) with parchment paper.
In a large bowl, whisk together the flour, brown sugar, baking powder, baking soda, and salt. Using a pastry blender or clean fingers, cut the butter in until the mixture resembles coarse cornmeal with some pea-sized lumps of butter remaining.
In a separate bowl, whisk together sweet potato puree, buttermilk and maple syrup. Stir into the flour mixture until just combined. Switch to kneading the dough to finish bringing it together.
2/3 cup cold buttermilk, 2 tablespoons cold maple syrup
Turn out the dough onto a lightly floured surface. The dough should be sticky but workable. If the dough is too sticky, kneed in an additional 1-2 tablespoons of flour. Pat or roll the dough until it’s approximately 1-inch thick. Cut the biscuits using a 3-inch cutter. Re-roll the scraps as needed to cut the remaining biscuits.
Place the biscuits on the prepared sheet pan and brush with melted butter. Bake for 12-15 minutes, until fluffy and golden brown.
1 tablespoon unsalted butter
Notes
Save time by cooking and pureeing the sweet potatoes the day beforehand, so there's no waiting for them to cool.