01 - Heat the milk in a saucepan until it reaches a gentle simmer. In a separate bowl, whisk egg yolks, sugar, cornstarch, vanilla, and salt until smooth. Gradually pour the hot milk into the egg mixture while whisking continuously. Return the combined mixture to the saucepan and cook over medium heat, stirring constantly until thickened, approximately 3 to 5 minutes. Remove from heat, cover the surface with plastic wrap to prevent a skin from forming, and allow to cool to room temperature.
02 - In a chilled bowl, beat the cold heavy cream with powdered sugar until medium peaks form, ensuring a light but stable texture.
03 - Place half of the sponge slices evenly at the base of a trifle dish or individual glasses. Spread half of the cooled custard over the sponge layer, then top with a layer of whipped cream. Repeat the sequence with the remaining sponge, custard, and whipped cream to form multiple layers.
04 - Refrigerate the assembled dessert for a minimum of 1 hour to allow the flavors to meld and the layers to set firmly.
05 - Just before serving, decorate the top with fresh berries, chocolate shavings, and chopped nuts as preferred to enhance visual appeal and flavor.