Preheat oven to 350. Mix all dry ingredients, using 1/4 cup brown sugar and setting the rest aside. Whisk 1 tablespoon milk, 2 tablespoons melted butter, applesauce, and egg. Stir into dry mixture. Pour batter into a gallon-sized plastic bag and cut the corner off. Pipe the batter into a greased mini-donut pan, filling each donut space about 1/2 full (for me, this was about 24 mini donuts). Bake for about 7 minutes. Remove from oven and take each donut out of the pan. Melt remaining 2 tablespoons butter with 1/4 cup brown sugar in a small saucepan over medium heat. Stir in chocolate chips until melted. Bring to a boil and boil for about 2 minutes. Add 1 tablespoon milk and bring back to a boil. Add powdered sugar, using the last tablespoon of milk to help thin out the frosting if needed. Keep over low heat (otherwise it will start to crystallize) and dunk each mini donut into the frosting. Frosting should set almost immediately, so sprinkle each donut right away.