4 1/2 cups unsalted butter, melted, cooled to room temperature
9 (18.25 ounce) boxes devil’s food cake mix
6 3/4 cups creamy peanut butter, warm
2 1/4 pounds large marshmallows, quartered
Preheat oven to 350 degrees F.
Combine butter and dry cake mixes in a bowl until crumbly. Reserve 7 pounds of mixture. Pat remaining crumb mixture into 9 ungreased 9 x 13-inch pans or equivalent.
Combine peanut butter and marshmallows in a bowl. Spread evenly over crumb mixture in the pans. (If space and bowls are a problem, mix each cake mix separately.) Crumble reserved cake mixture over top and bake 20 minutes. Let cool before cutting into bars.