250g brown sugar
375g can sweetened condensed milk
100g butter cubed
2 tbps liquid glucose (available in the baking section of the supermarket)
200g dark cooking chocolate finely chopped - best quality you can afford.
Mix everything except the chocolate together in a glass bowl and place in the microwave for 3 minutes. Take it out and stir with a metal spoon. Place in microwave for 2 minutes. Stir again. Repeat until the mixture has been cooked 5 times.
Stir, allow bubbles to go down and the whole thing to cool a bit and then add the chocolate. Mix until melted. Pour the mixture into a slice tin lined with foil or baking paper. Set in the fridge.
I mark cutting lines into it before it goes completely hard.
Then... try not to eat it all at once.