1Heat oven to 350°F (325°F for dark or nonstick pan). Grease bottom only of 8-inch or 9-inch square pan with shortening or cooking spray. Make brownie batter as directed on box--except stir in 2/3 cup of the chocolate chips. Spread in pan.
2Bake brownies as directed on box. Immediately after removing from oven, sprinkle with 1 to 1 1/3 cups miniature marshmallows, remaining 2/3 cup chocolate chips and the peanuts. (For softer marshmallows, cover pan with cookie sheet about 2 minutes.) Cool completely, about 2 hours. For 16 brownies, cut into 4 rows by 4 rows with knife dipped in hot water. Store tightly covered