Thanks to Dave, Daisy and George in Carlisle for this.
Boil 2 small cans of condensed milk for 90 minutes. Have faith they will not explode, and use an old saucepan – when we did this a bit of the paint came off the tins. Better still try and find tins with paper labels.
Crush about 250-300g biscuits to a medium fine crumb – either digestives or ginger or some of each. Add 125-150g melted butter, push firmly into the base of a dish, making a layer about 1cm thick. Leave to set.
Chop enough bananas to make another layer 1cm on top of the biscuit base. Open the tins of condensed milk – the contents will have magically turned to toffee. Spread over the bananas, top with cream and grate chocolate on top.