Crush the biscuits in a plastic bag with a rolling pin as finely as possible.
Mix half the butter with the biscuits and mixed spice. Using a spoon, press into the base of
18-20cm / 7-8 in flan pan lined with plastic film. Chill to set.
Put the remaining butter in a pan, add the condensed milk and bring to the boil, stirring all
the time or it will burn. Reduce the heat and simmer for 5-6 minutes, slowly stirring, until you
have a light golden colour. Remove from the heat, beat in 2 tablespoons of the double cream and
leave to cool.
Pour this caramel on top of the biscuit base and arrange half the banana slices on top of the
caramel. Put another layer of banana on top of that. Sprinkle with cocoa powder, then chill.
When ready to serve, whip the remaining double cream, spoon this on top, and dust with more
cocoa powder to serve.