To save some time, start boiling the water first. While you're waiting for the water to boil, start cooking the sausage and fennel. By the time the sausage and fennel is finished, the water should have boiled, and while the pasta is cooking, chop the onion and mix the sugar and vinegar in a small dish. Now it will be time to add the sausage/fennel to the pasta. Give it a stir. Next step is to cook the onion and get the tomato cream sauce cooking. While the sauce is simmering, grate the fontina on a piece of parchment paper (makes cleanup SUPER easy!), and the Parmesan (on a separate piece of parchment).