In the dutch oven, render the pancetta over medium heat. Theres no need to add oil into the dutch oven since the pancetta fat will render out. Continue cooking until pancetta is nice, browned, and crisp. This means the pancetta has rendered properly. Remove the pancetta from the dutch oven, set aside, and leave the leftover fat in there.
Add the mushrooms and a couple sprigs of fresh thyme to the dutch oven with the pancetta fat and cook sauté over medium heat until mushrooms are tender and the water from the mushrooms have evaporated. Add white wine to deglaze the pan and cook until wine wine has evaporated. Salt to taste. Discard thyme stems, remove mushrooms and set aside.
Clean out the dutch oven and put it back over stove on medium heat. Add butter and flour and mix until it forms a paste to create the roux for the mornay sauce. Slowly whisk in milk little by little until milk and roux have incorporated well. Continue whisking mixture a but as the mixture comes to a boil and begins to thicken. Mix 2 tsp. of cornstarch with 2 tsp. water and drop it into the mixture, while whisking and waiting for it to thicken a little more.
When the mixture is thickened, turn the heat down to low and gradually add in shredded fontina, gruyere, and parmesan a little at a time. Leave about 1 cup for crust. Whisk to combine well into a smooth sauce. Add mushrooms and pancetta in. Salt and pepper to taste.
While the mornay sauce is cooking, bring a pot of water to boil over high heat. Salt water generously and add a tbsp. of olive oil. Boil dried rotini pasta according to instructions on packet or until the pasta is almost al dente, but still a little underdone.
When pasta and mornay are done. Add cooked pasta into the dutch oven with the mornay and stir to combine. Top the pasta with the reserved shredded cheese and spread across entire surface.
Bake at 375°F (190°C) for 15 minutes.
Bake the pasta at 375°F (190°C) for 15 minutes or until rust is bubbling and golden brown.
If you’d like to add a parmesan chip. Take a spoonful of shredded parmesan per chip and spoon it onto aluminum foil over a baking sheet. Arrange about 1 tbsp. of cheese about 2″ away from each other to give room for spreading. Put this in the oven as well and cook for 5-10 minutes, or until cheese has browned and formed a crust. Remove and chill chip for at least 15 minutes before serving.
Garnish mac and cheese with parmesan chip and fresh parsley. Congrats! You just made mac n’ cheese.