1Grease bottom only of square pan, 9x9x2 inches or 8x8x2 inches, with shortening or cooking spray. Heat oven to 350°F for 9-inch pan, 325°F for 8-inch pan.
2Make brownie mix as directed on box, using water, oil, eggs and adding 1 teaspoon cinnamon. Spread batter in pan. Bake as directed on box. Cool completely, about 1 hour.
3Heat hot fudge topping over low heat until warm. Stir in 1/2 teaspoon cinnamon. Serve brownies topped with ice cream and hot fudge topping.