Mars Bars Square

4 Mars chocolate bars
1/2 cup butter or margarine
3 cups Rice Krispies cereal

Topping:
1 cup semi sweet chocolate chips
1/2 cup butter or margarine.

Heat chocolate bars and butter together in large pan, stirring often until melted. Remove from heat, add rice krispies, stir to coat. Press in greased 9x9 pan. Chill. For the topping, combine chocolate chips and butter in small saucepan over low heat, stirring often until smooth. Spread over square. Chill. Cut into squares.