Preheat the oven to 350 degrees F.
In a large pot, bring the water to a rolling boil. Add the salt. Taste the water. It should be salty like sea water. Add the macaroni and stir, with a wooden spoon or large slotted spoon, to ensure the macaroni does not stick to the bottom of the pot as it cooks. Cook until the macaroni is still quite firm, 8 to 10 minutes.
Pour the macaroni and water into a strainer placed over the sink. Allow the water to drain out, reserving approximately 1 cup of the liquid.
In the same pot, bring the cream, garlic cloves, and the reserved cooking liquid to a simmer. Add the mustard and 3 cups of the Gruyere. Season with salt and pepper, to taste. Simmer gently, stirring constantly, until the cheese is melted and has integrated with the cream. Add the Parmesan and Cheddar. Stir with a wooden spoon and simmer again until smooth. Add a splash of Worcestershire and a splash of hot sauce. Stir to blend. Taste for seasoning.
Add the macaroni to the cream and stir gently to blend. Allow the macaroni to rest on the stove, 5 to 10 minutes, so the pasta absorbs the flavors. Remove and discard the garlic cloves.
Fill a baking dish with the macaroni mixture, top with the bread crumbs, the remaining Gruyere cheese and bake 10 to 12 minutes or until the bread crumbs crust on top. Serve immediately.
Recipe courtesy of Alex Guarnaschelli