Heat the oven to 180C/fan 160C/gas 4.
Crush the biscuits in a food processor then add the melted butter and pulse to combine. Press the mixture into a 24cm tart tin, with a removable base, in an even layer.
Transfer the tin to a baking sheet and cook for 10-12 minutes, until lightly toasted and set.
Leave to cool then gently release from the tin and put on a serving plate. 
Spread the condensed milk over the biscuit base and chill for 1 hour. Arrange the banana slices over the toffee. Whip the cream and sugar together to form soft peaks and spread over the bananas. Melt the chocolate in a microwave or in a bowl set over, not in, a pan of simmering water. Allow to cool slightly, before drizzling over the cream