Make the biscuits: Beat the sugars and butter until well combined. Beat in the egg and vanilla. Whisk the flour, baking powder, and salt in a separate bowl, then stir into the butter mixture. Heat the oven to 200C (180C fan)/390F/gas 6, and line two baking trays with greaseproof paper. Tear off small pieces of the dough, roll these into balls, then arrange on the trays spaced well apart. Bake for 18-20 minutes, until golden brown, then remove and leave to cool completely.

Make the vanilla custard: Slit the vanilla pod down its length, scrape out the seeds, and put these and the empty pod in a large saucepan with the milk. Bring to a simmer, then turn off the heat and leave to infuse for about an hour. Whisk the egg yolks, sugar, and cornflour in a heatproof bowl set on a damp cloth or similar to anchor it to the workspace. Bring the milk back to a simmer, remove, and discard the spent vanilla pod, then pour a little of the hot milk into the egg yolk bowl, whisking as you do so. Continue adding the milk bit by bit until there’s about a quarter of it in the bowl, then pour the lot into the milk pan and heat again, stirring continuously, until the mix thickens. Once the custard begins to bubble on top, cook, still stirring, for just another 90 seconds (set the timer), then take off the heat and leave to cool. Once cool, stir in the vanilla extract.

Prepare the bananas: Peel the bananas and cut them into 1cm-thick slices. Heat the butter in a large frying pan until foaming, then stir in the sugar and nutmeg if using. Add the sliced bananas, toss to coat for a minute or so, then take off the heat.

Build the pudding: Fill the base of a large glass dish with a quarter of the custard. Top with a layer each of half the biscuits and half the bananas, then repeat. Finish with a layer of custard, cover, and chill for at least two hours and preferably longer.

Finish with the topping: Whip the cream to soft peaks, then fold in the soured cream if using. Dollop this on the top layer of set custard and finish with the peanuts or pecans if using; crumbled cookies, a sprinkling of nutmeg or cinnamon, or a few extra pieces of banana tossed in lemon juice also work well as toppings.