Peel and coarsely chop the onion. Dice the pancetta and peel and chop the sausage.
Cut tomatoes in 4, or more if you are using big tomatoes instead of cherry.
Heat the olive oil in a medium/large pan and add the chopped onion, the pancetta, and the sausage. Cook a couple of minutes or until the sausage is completely cooked. Add tomatoes, a pinch of salt and pepper, and cook, medium heat, for about 10 minutes.
Meanwhile, bring pasta water to a boil.
Mix the egg yolk, cheese, and milk in a large bowl.
Once the pasta is cooked, drain it and pour it into the skillet, sautè a couple of minutes, turn off the heat and add the yolk and cheese mixture.
Mix well and serve hot.