Begin with the crème pâtissière. Heat the milk and vanilla bean seeds in a small saucepan – keep an eye on it, as milk overflows easily! In a medium bowl, whisk the egg yolks and sugar until pale, then whisk through the cornflour.While whisking continuously, gradually stream the hot vanilla milk into the egg yolk mixture until fully combined. Return the custard base to the saucepan and cook, whisking, until the mixture thickens and begins to bubble. Remove from the heat, then strain with a fine mesh sieve into a large bowl (to remove any egg lumps). Whisk through the butter. Press a sheet of plastic wrap directly onto the hot custard (to prevent a skin from forming), then refrigerate until completely chilled.While the custard chills, pour the cream into a second large bowl. Use an electric hand mixer to whip the cream to soft peaks, then cover and refrigerate until needed. Once the crème pâtissière is cold, whisk in a little of the whipped cream, then switch to a flexible spatula and fold in the remaining cream to make the crème légère.Place a few scoops of the crème légère into the base of a large trifle bowl. Add a handful or two of savioardi biscuits (reserve a few to garnish!), then add a handful of sliced banana, then repeat the layers, finishing with a layer of crème légère. Cover and refrigerate for 6 hours, then scatter with crushed savioardi and serve.Photography by Jiwon Kim.Want more from The Cook Up? Stream all the seasons here and for free at