Crockpot Rice Crispy Treats

In a crockpot place:
3 tablespoons butter or margarine
4 cups miniature marshmallows
6 cups Rice Krispies®
1/2 C peanut butter
Turn the crockpot on high for 1 hour. Remove and place with a spatula into a greased 9"X13" pan. In a pan melt 1 package of semisweet chocolate chips. Spread on the top of the Rice Crispy treats. Top with 1/2 C chopped peanuts. Set aside to cool.