This dessert is not a classic trifle. I serve it in small votive-type candle holders. This recipe makes about 16 individual "mini" servings.
Heat milk and 2/3 cup of cream in a heavy saucepan. Meanwhile, in a double boiler, whisk the eggs, sugar and flour until smooth. Slowly whisk in hot milk mixture, being careful not to "cook" the eggs.
Continue to stir the custard until it thickens slightly, about 10 minutes. Set the bowl on ice, and chill the custard, whisking every few minutes. Stir in the vanilla, and set aside.
Combine the remaining cream, espresso powder and half the rum (3 tbsp) in a mixer and whip to firm peaks.
Gently fold a third of the coffee cream into the cooled custard; repeat until all the cream has been incorporated.
To assemble, place a layer of pound cake in the bottom of each dish, topping with a few slices of banana, and a tablespoon or more of the custard. Lay one more layer of cake and banana on top, then drizzle all the dishes with the remaining rum.