350 g (11 1/2 oz) shop-bought fresh vanilla custard
25 g (1 oz) pecan nuts, chopped
Beat together the mascarpone and 2 tablespoons of the liqueur in a bowl and chill.
Meanwhile, divide the cake between 4 glasses, then drizzle each with 1 tablespoon of the liqueur. Add the bananas, reserving 4 slices for decoration, then drizzle each with 1/2 tablespoon of the toffee sauce. Spoon over the custard and top with the mascarpone cream.
Drizzle with the remaining toffee sauce and decorate with the reserved banana slices and pecans. Serve immediately.