Melt-It - Melt margarine in large saucepan over low heat. Add marshmallows and stir until completely melted. Remove from heat.
Mix-It - Add Rice Krispies cereal, stir until well coated.
Spread-It - Using buttered spatula or waxed paper, press mixture evenly into 13 by 9 by 2 inch pan coated with cooking spray. Cut into 2 by 2 inch squares when cool.