1 package spice cake mix
3/4 cup cooked, mashed sweet potato
1/4 cup buttermilk
1-2 cups all purpose flour
Canola oil for frying
1 1/2 cups sugar
1 Tablespoon cinnamon
Mix the cake mix, sweet potato and buttermilk together in a large bowl.
Stir in the flour, 1/2 cup at a time, until you have a soft dough.
Turn dough out onto the counter and knead gently, adding enough flour to make a dough that does not stick to the countertop.
Dust counter with more flour, and roll dough out into a rectangle about 3/4 inch thick.
Let dough rest for five (5) minutes.
While the dough is resting, heat several inches of oil to 350°F.
With a doughnut cutter (or one large and one small biscuit cutter) cut out the doughnuts and place them on a cookie sheet lined with wax paper.
Gather up scraps after cutting out as many doughnuts as possible, knead gently, let rest, then re-roll dough and cut more.
You can save the doughnut holes and fry them too, or reroll them to make more doughnuts.
Fry doughnuts in batches, turning once, until dark golden brown and puffed, about 3-4 minutes.
Drain doughnuts on paper towels briefly.
Stir cinnamon into sugar in a shallow bowl.
Dip warm doughnuts into the cinnamon sugar, turning to coat both sides.
Makes about 16 doughnuts, depending on size.