Prepare the shortcrust pastry quickly kneading together all of the ingredients to obtain a smooth dough, then allow it to rest in the refrigerator for one hour. Continue by preparing the pastry cream and the meatballs, the size of walnuts, using 200 g of boiled and ground chicken meat mixed with 1 egg, 2 tbsp parmesan cheese, chopped parsley and a pinch of salt. Fry the meatballs then put off to the side. Sauté the chicken in a bit a butter, adding the liver, sausage, mushrooms, meatballs and peas and cook for a few minutes. Transfer the mixture over to a casserole dish, adding a few spoonfuls of meat sauce, and allow to cook for a few more minutes. In the meantime, boil the maccheroni until tender yet still quite firm, drain then toss with the meat sauce, butter, a generous amount of parmesan cheese and allow to cool. Butter a ring-shaped mould with a diameter of 30 cm and cover the bottom and the sides with a third of the pastry dough to form a layer about ½ cm thick. Be sure that the pastry sticks out a bit from the sides in order to easily close the timballo with the other layer of dough. Place half of the maccheroni on top, spread the meat, sliced boiled eggs and the parmesan on top then cover with the rest of the maccheroni, giving the pasta a domed shape over which you will pour the pastry cream, making sure it penetrates thoroughly. Cover the timballo with the remaining shortcrust pastry. Brush the surface with the beaten egg and bake for approximately 45 minutes in a 180°C oven. Allow the timballo to cool for at least 15 minutes before removing the ring and serving.