Whisk together sugar, baking powder, cinnamon, applesauce, milk, and flour until no lumps remain. You should have a fairly thick batter.
In a shallow bowl, mix together cinnamon and sugar until combined. Set aside.
Preheat ~½ inch of oil in a pan to 350F.
Using a mandolin slicer or a knife, slice apples ~¼ inch thick. Use cookie cutters to cut rings out of the slices. Coat rings with batter and fry until golden on both sides (about 2-3 minutes per side).
Let drain briefly on a plate lined with paper towels.
Dunk fried rings into the cinnamon sugar and set on another paper-towel-lined plate.
Serve immediately!