Step 1

Grease a 18cm x 28cm slice pan. Line base and two long sides with baking paper, extending paper 5cm above edge of pan.

Step 2

Place Mars Bar and butter in a medium saucepan. Stir over low heat for 5 minutes or until melted.

Step 3

Place Rice Bubbles in a large heatproof bowl. Add Mars Bar mixture; stir to combine. Press mixture firmly into pan. Refrigerate until firm.

Step 4

Combine chocolate and oil in a medium heatproof bowl. Place bowl over a medium saucepan of simmering water (don't let water touch base of bowl); stir until chocolate is melted and smooth. Spread evenly over slice. Refrigerate until set.

Step 5

Using a hot knife, cut into small bars.