Preheat oven to 450°F. Place an oven rack in the center position of the oven.
In a medium mixing bowl combine flour, baking powder, salt, and sugar.
1 ¼ cups flour, 1 tbs baking powder, ½ teaspoon salt, 2 tbs sugar
Cut your butter into small pieces then cut it into the flour mixture by using a pastry cutter, forks, or by pressing pieces of the butter between your thumb and pointer finger in the flour (like in my flaky pie crust). I like to grate the butter into small pieces- it makes cutting in much easier.
6 tbs unsalted butter
Mix in the mashed sweet potatoes until a soft dough forms.
¾ cups mashed sweet potato*
Stir in milk 1 tbs at a time until the dough really comes together. The amount needed will depend on how wet the sweet potatoes were (ie from a casserole vs freshly cooked and mashed).
2-3 tbs cold milk
Turn dough out on to a lightly floured surface and knead until in holds together.
Smooth dough out with a roller or just by patting, until it is ½ inch thick. Cut into circles with a drinking glass, or a biscuit cutter.
Place biscuits on a parchment lined baking sheet and bake for 12-17 minutes, or until golden brown. Check the biscuits at 12 minutes, carefully look at the bottom of one of the biscuits- if they are lightly browned they are done. Be careful not to burn yourself while checking.