1Line a tin with baking paper, ensuring the paper overlaps the sides.
2Unwrap 7 1/2 Mars bars, roughly chop them, and place them into a bowl.
3Weigh out 260 grams of butter and add it to the bowl with the Mars bars.
4Melt the Mars bars and butter together in the microwave for 5 minutes.
5Remove from microwave; mix should be bubbled. Fold the mix with a spatula, then whisk to combine.
6Pour in 220 grams of rice bubbles and fold them into the mix.
7Pour the mixture into your prepared tin and flatten it evenly using a spatula and a chopping board to compress.
8Place in the fridge for 3–4 hours or freezer for 45 minutes–1 hour to set.
9Break up 520 grams of cooking chocolate into a bowl and microwave for 1 minute at a time, stirring in between until melted.
10Pour the melted chocolate onto the set rice bubble base and spread it evenly with a spatula.
11Add chopped Mars bar pieces on top to decorate.
12Leave in a cool place to set for 30 minutes–1 hour. Once set, lift the slice out of the tin and cut into even slices using a ruler to measure and divide evenly. Keep dragging the knife over the lines to prevent the slice from cracking.