Preheat oven to 425°F. Prepare baking sheet with parchment paper.
In large bowl, stir together flour, baking powder, salt, sage and smoked paprika. Using a pastry blender or two forks, cut in butter until mixture resembles coarse crumbs.
In medium bowl, whisk together buttermilk and mashed sweet potato. Stir into flour mixture until a dough forms.
Turn dough out onto floured surface and knead 3-4 times or until dough comes together. Roll dough to 1 in. thickness and cut into 16 squares with a 2 in. square cutter, re-rolling dough as necessary. Place biscuits onto prepared pan and brush with buttermilk. Bake 15-17 minutes or until golden brown. Serve warm.