The old-school-y-ness of this recipe can be seen by the fact that the quantities are in ounces. With thanks to my mum for giving me the recipe.
The quantities couldn’t be simpler – you need one ounce of rice crispies and salted butter per large Mars bar. For a standard sized rectangular cake tin, use 4 ounces of rice crispies, 4 ounces butter and 4 large Mars bars.
I tend to double this – using the large rectangular dishes that are roughly the same size as one full oven shelf (8 oz. rice crispies, 8 oz. butter, 8 Mars bars).
You will also need some dark chocolate to melt over the top – approx. 150-200g for the ‘4 bar’ size, and 300-400g for the ‘8 bar’ size.
Chop the chocolate bars finely, and melt them slowly with the butter in a bain marie or large heatproof bowl over a pan of simmering water. Be careful that no steam from the water goes into the buttery-chocolate. Once the chocolate and caramel has melted, you will need to take the bowl off the heat and give it a good stir/pound to break down the little lumps of nougat and create a smooth consistency – if you do this on the heat, the chocolate will be at risk of splitting.
When the chocolate mixture is smooth, quickly mix in the rice crispies and press into a flat, shallow cake tin/foil dish (as described above). It may look like not enough goo to make the squares chocolatey enough, but trust me it does.
Leave the rice crispies to set in the fridge, and cover them with a layer of melted dark chocolate when completely set – ie. the next day. Leave to set and cut into squares to serve.