Line an 8x8 inch square baking pan with parchment paper.

In a large saucepan over low heat, melt the chopped Mars bars and 1/2 cup butter, stirring constantly until smooth.

Remove from heat and immediately fold in the puffed rice cereal until evenly coated.

Press the mixture firmly and evenly into the prepared baking pan.

In a microwave-safe bowl or double boiler, melt the milk chocolate and 1 tablespoon of butter together until smooth.

Spread the melted chocolate evenly over the cereal layer.

Refrigerate for at least 30 minutes or until set.

Cut into 16 squares and serve at room temperature.