12 ounces plain dark chocolate (I actually use half plain and half milk)
4 ounces butter
14 ounces condensed milk
8 ounces digestive biscuits (broken)
Line a cake tin with clingfilm/greaseproof paper. I vary the tin depending on the event - a loaf-style cake is better for home use, cookie trays are easier for slicing up for a pot luck, or a regular round cake tin is fine if you're using the cake for a birthday. Melt the chocolate and butter in a large heatproof bowl (either over a pan of simmering water, or you can nuke it in the microwave in 10-second bursts). Pour the condensed milk into the chocolate and butter mixture and beat together until creamy. Add the broken biscuits and mix well. Pour the mixture into the cake tin and press it well into the corners. Leave to cool a little then refrigerate until set (it usually takes at least 2 hours depending on how cold your fridge is).