Cook the spaghetti in plenty of boiling salted water according to the instructions on the packet. Dice the bacon, peel the garlic and onion, chop finely. Clean and wash the zucchini and cut into small cubes. Clean the mushrooms and cut them in slices. Fry the bacon in hot olive oil. Add the garlic and onion cubes, zucchini and mushrooms and sauté. Pour in the milk and cream and bring to the boil. Add the Bresso cream cheese to the vegetable sauce and melt while stirring. Whisk the egg yolks with a little sauce and add to the hot, no longer boiling vegetable sauce, season with salt and pepper. Drain the spaghetti, drain well and mix with the vegetable and cheese sauce. Serve sprinkled with basil leaves.