Prepare a slice tin by lining with baking paper and set aside.
In a glass bowl, place butter and Mars Bars. Heat in the microwave for 1 1/2 minutes and remove to stir.
Pour Rice Bubbles into the butter/Mars Bar mixture one cup at a time mix. Mix until all combined.
Press into the slice tin with the back of a large metal spoon. Set aside.
Break the block of chocolate into small squares and microwave for 1 minute and stir for 30 seconds. Heat for 20 seconds more if it doesn’t become smooth and creamy.
Pour the melted chocolate over the Rice Bubbles mixture and spread evenly.
Cool in fridge until chocolate hardens. Lift slab out of tray with baking paper place on cutting board.
Once it is room temperature, cut into squares with a large sharp knife.
