Break the Mars Bars up and place them together with the butter in a saucepan. Heat it over medium heat until it has all melted together. Remove the pan from the heat and stir in the rice bubbles until they are all coated.
Spread the mixture into a lined tin and drizzle with melted chocolate.
Refrigerate for at least one hour then remove and cut into squares. Store it in the fridge.
Notes
Mars Bar Slice Variations
Double Chocolate Mars Bar Slice: Add ½ cup of dark chocolate chips to the mixture for an extra chocolatey treat or drizzle the finished bar with extra melted dark chocolate.
Nutty Mars Bar Slice: Mix in ½ cup of chopped peanuts or slivered almonds for added crunch.