Prepare the custard: In a saucepan, heat the milk until it begins to simmer. In a separate bowl, whisk together the egg yolks, sugar, and cornstarch until well combined. Slowly pour the hot milk into the egg mixture while continuously whisking. Return the mixture to the saucepan and cook over low heat, stirring constantly, until it thickens into a custard consistency. Remove from heat and stir in the vanilla extract. Allow the custard to cool.

Assemble the layers: Slice the sponge cake or ladyfingers into thin, even slices. Dip each slice into the liqueur, ensuring they are well soaked but not overly saturated. Layer half of the soaked cake at the bottom of a glass dish or individual serving glasses. If desired, add a layer of sliced fruit or nuts on top of the cake.

Add the custard: Pour half of the cooled custard over the cake layer, spreading it evenly. If using fruit or nuts, ensure they are evenly distributed. Repeat the process with another layer of soaked cake and the remaining custard.

Top with chocolate custard: Finish the Zuppa Inglese by spreading a layer of chocolate custard or chocolate pudding over the final layer of custard. Smooth it out to create an even top layer.

Chill and serve: Cover the dish or glasses with plastic wrap and refrigerate for at least 2-3 hours, or until the dessert is firmly set. Before serving, you can garnish with additional fruit, grated chocolate, or a sprinkle of cocoa powder.