Preheat oven to 450 degrees F and butter a 9 by 13-inch glass baking dish.
Bring a large pot of water to a boil and add salt. Cook macaroni according to package directions. Drain.
In a large Dutch oven or other heavy pot, saute the bacon until crisp. Remove bacon with a slotted spoon and reserve. Saute the onion in the bacon drippings until soft. Add the 5 tablespoons butter to the onion mixture and melt the butter stirring with a wooden spoon.
Using a whisk, add the flour, and stir constantly until well mixed with the fat making a roux. Whisk in the mustard. Gradually add the milk and cream whisking constantly.
Add the thyme, bay leaf, and salt. Let come to a simmer and stir frequently for 15 minutes.
Strain the hot milk mixture into a metal bowl and discard the solids. Working quickly, mix in 1 cup fontina, blue cheese, 1/2 cup Gruyere, 1/2 cup white Cheddar, 1/2 cup Parmesan, the reserved bacon, and parsley. Continue to stir until all cheese is melted.
Add the cooked noodles to the cheese mixture to coat. Add the noodle mixture to the prepared baking dish. Mix the remaining cheese and bread crumbs together and sprinkle on top of the noodles. Bake for about 15 to 20 minutes or until bubbling and golden brown. Remove from oven when done and rest for 5 minutes.