i don't know, i've been making this for years and years. this is my signature treat

• 150 g rice krispies (cheapest kind)
• approx 200-250 g Mars Bars (about 7 small 33 g ones, or 5-6 of the standard 40 g ones), cut into small pieces
• 100 g salted butter
• 25 g golden syrup
• 200 g good quality cooking chocolate

1. Line a container with greaseproof paper, leaving some hanging over the edge to use as handles.
2. In a bowl that's big enough for 150 g rice krispies, melt mars bars, butter, and syrup together in a microwave or bain-marie. It's fine if the caramel doesn't melt fully, but try and break it up with a spatula or something.
   
   100 g butter
   25 g golden syrup
   200-250 g mars bars
   
3. Mix in rice krispies. Coat thoroughly
   
   150 g rice krispies
   
4. Transfer into the tray. Compress firmly with a potato masher, especially at the corners.
5. Melt chocolate and pour over the for the topping.
   
   200 g cooking chocolate
   
6. Set in fridge, at LEAST overnight, then cut into small squares.

• Have not measured the tray i use but would guess that it is about 10x10 inches ish? Gives 25 squares. Larger trays give thinner pieces but also thinner chocolate layer.
• Sainsburys belgian milk cooking chocolate is the best cooking chocolate i've tried
• Consider melting the mars bars slightly before adding the butter (as the butter will melt much more quickly)

• you could probably use multiple different chocolates for the topping. do a fancy marble pattern, even.