Make the ragu sauce first. Heat the oil in a large skillet over medium heat and add the carrot, onion and celery. Season with salt and pepper and sweat until the vegetables are soft, about 10 minutes. Add the meat and cook slowly until cooked through. Add the tomato sauce and cream and stir together. Bury the cheese rinds in the sauce and cover; simmer while you prep everything else.
Spray the inside of a large metal bowl (mine is 13 inches across and 5 inches high) and dust liberally with the breadcrumbs. Cook the pasta sheets one at a time in salted boiling water; carefully lift out and drape them around the bowl, leaving a generous amount overhanging to cover the bottom.
Toss half of the ziti with the béchamel sauce and 1 cup of the Parmigiano cheese and the other half with ⅔ of the ragu. Reserve the rest of the ragu sauce to layer in the Timpano.
Layer the prosciutto slices over the pasta layer, then spoon in the ziti with béchamel sauce, pressing it up the sides into an even layer. Add the meatballs next then cover with the reserved ragu sauce and half of the mozzarella. Lay the basil leaves on top of the cheese
Cover this layer with the ziti in ragu sauce, then ress the eggs into the ziti around the edges of the bowl and layer the remaining mozzarella and Parmigiano cheeses over the top. Fold in the edges of the pasta to create the base of the Timpano and spray with cooking spray.
Bake, covered with foil or a large lid, at 300 degrees until the Timpano reaches an internal temperature of 120 degrees. If you refrigerate the Timpano, be sure to bring it back to room temperature before baking.
When heated through, carefully invert onto a cutting board and gently lift the bowl off. Let stand for 10 minutes before slicing and serving with the marinara sauce and cheese.
Recipe by Cooking With Michele® at https://cookingwithmichele.com/2020/01/the-big-night-timpano-timballo-for-a-crowd/