Mars Bar Chocolate Slice

3 large Mars Bars
90g butter
200g block chocolate
3 cups rice bubbles
Melt Mars Bars in 90g butter in large saucepan on low heat. Stir continuously until smooth. Pour in rice bubbles. Press into tray (lamington tray 19 x 29cm). Melt chocolate in 30g butter in microwave until smooth (Low). Pour over the top. Refrigerate. When set, do pattern.