Heat oven to 325°F (350°F for glass pan). Line 9-inch square pan with foil, letting foil hang 2 inches over sides of pan. Grease bottom and sides of foil with shortening or cooking spray. Make brownie batter as directed on box. Spread in pan.
Bake 37 to 42 minutes (34 to 39 minutes for nonstick pan) or until toothpick inserted 2 inches from side of pan comes out almost clean. Cool completely on cooling rack, about 1 hour 30 minutes. Freeze in pan 30 minutes. Using foil to lift, remove brownies from pan, and peel foil away.
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