Preheat oven to 450°. Stir together first 5 ingredients and 1/2 tsp. cinnamon in a large bowl; cut in butter with a pastry blender until mixture resembles small peas and dough is crumbly. Freeze 5 minutes.
Stir together sweet potatoes and 1/2 cup whipping cream. Add to flour mixture, stirring until dry ingredients are moistened.
Turn Dough out onto a lightly floured surface (mixture will be crumbly); knead 1 minute. Pat dough into a 3/4 -inch-thick circle. Cut dough with a well-floured 2-1/2 inch round cutter. Rerolling scraps as needed.
Line baking sheets with parchment paper; lightly grease paper with cooking spray. Place biscuits 2 inches apart on prepared baking sheets. Brush tops for biscuits with the 2 Tbsp. of whipping cream.
Stir together granulated sugar and remaining 1/4 tsp. cinnamon. Sprinkle dough rounds with sugar mixture.
Bake at 450° for 13-15 minutes or until golden brown.