In a small bowl, stir together ⅓ cup warm water and yeast. Let stand until mixture is foamy, about 5 minutes.
In a medium bowl, whisk together flour, sugar, baking powder, and salt. Using a pastry blender, cut in cold butter until mixture is crumbly. Add yeast mixture and sweet potato purée, stirring with a fork just until combined.
Turn out dough onto heavily floured surface, and knead until well combined. Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let stand in a warm, draft-free place (75°) until dough is puffed, about 30 minutes.
Preheat oven to 400°. Line a large baking sheet with parchment paper.
On a lightly floured surface, turn out dough, and pat to ¾-inch thickness. Using a 2¼-inch round cutter dipped in flour, cut dough, rerolling scraps as necessary. Place on prepared pan.
In a small bowl, whisk together egg and 1 teaspoon water. Brush egg wash onto dough.
Bake until golden brown, 12 to 14 minutes. Serve warm.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/caramelized-onion-gravy-sweet-potato-angel-biscuits/