Boil the elbow macaroni in a large pot in salted water according to package directions. Save a half cup of the starchy pasta water and set aside. Pour the macaroni into a pasta strainer and rinse very well with cold water so it doesn't become mushy.

Set the same large pot over high heat and add the quart of heavy cream, kosher salt, and pepper. Bring to a boil, watching carefully as it will bubble up (if bubbles too much remove from heat for a moment).

Once boiling, reduce the heat to medium low and cook 30 minutes, stirring several times and scraping the sides a few times.

Use a box grater to shred the cheese. Once the cream has cooked for 30 minutes it should be reduced by half. Add the cooked pasta, shredded Colby jack cheese and parmesan cheese, stir until melted.

Add 1/4 cup of the reserved pasta water and stir until combined. Taste for seasoning and add more kosher salt and pepper as needed. Add more of the reserved pasta water if you prefer a creamier mac and cheese.