If your ricotta is a bit lumpy or runny, let it drain for a good 20 minutes in a sieve and then press it through the sieve.
Separate the 3 eggs, adding the yolks to the ricotta and reserving the whites. Add the extra yolk to the ricotta along with the sugar and (if using) flour. Mix all these ingredients together until well amalgamated. If using, add one or more of the optional fillings and flavorings to the ricotta mixture, incorporating them very well.
Whip the egg whites until they are quite fluffy and stiff. The whites should retain its shape and stand up by themselves like this:
Now add the whipped whites to the ricotta mixture. Fold the whites very gently into the mixture with a spatula, scooping the mixture from the bottom in a circular motion until you have a homogenous, fluffy mass.
Now grease the inside of a large mold (or individual molds—see Notes below) with butter and add cover them in breadcrumbs, shaking the mold around so that the breadcrumbs adhere and cover the inside surface completely. Turn the mold over and shake out any excess breadcrumbs.
Now add the ricotta mixtures to the mold, making sure not to overfill it, as the mixture will expand considerably as it cooks.
Bake the mold in a moderate oven (180C/350F) until the mixture is set and browned at the edges, about 30 minutes for individual molds, 45-60 minutes for a single large mold.
Let the pudding cool completely. Unmold it by flipping it over onto a baking tray, like so:
Serve your budino, if you like, with one of the suggested toppings.
