Preheat the oven to 425 degrees. Line a baking sheet with parchment or a baking mat.
Remove the skin from your cooked sweet potato. My favorite method to cook sweet potatoes is the crock pot or Instant pot. This post tells you exactly how to do it. You will need about 3/4 cup of sweet potato.
In a medium mixing bowl combine the flour, baking powder, and salt. Use a whisk to combine.
Add the butter, and then using a fork or pastry blender, work the butter into the flour mixture until it is the size of small peas. Refrigerate for 10 minutes.
While the flour/butter mixture is cooling, mash your sweet potato and buttermilk together. You can use a food processor if you want it extra smooth.
Gently combine the sweet potato mash and the flour mixture, until it combines into a dough. If the mixture is crumbly and not sticking together, add more buttermilk 1 tablespoon at a time, until the dough comes together.
Remove the dough onto a flour dusted surface and dust the top with a little more flour. Roll the dough so that it is 3/4 of an inch thick. Cut the dough using a knife or a biscuit cutter into 9 pieces.
Place the biscuits on the baking sheet and into the oven. Bake until the tops are a light golden brown, 12 to 15 minutes. Serve hot.