Kellogg's Rice Krispies Treats - Original

3 T butter
1 package {10 oz, about 40} regular marshmallows or 4 cups miniature marshmallows
6 C Kellogg's Rice Krispies cereal

Melt butter in large saucepan over low heat. Add marshmallows and stir until completely melted. Remove from heat. Add Kellogg's Rice Krispies cereal. Stir until well coated. Using buttered spatula or waxed paper, press mixture evenly into 9x13 pan coated with cooking spray. Cut into squares when cool. Melt chocolate chips for topping and spread evenly.