Preheat oven to broil. Grease 3-quart casserole dish. Over medium heat, warm the cream. In a separate pot, melt the butter and stir in the flour to make a roux. Cook roux two to three minutes and slowly pour in hot cream while whisking. Once mixture comes to simmer, slowly add grated cheeses, whisking until smooth between additions. Add salt, nutmeg, white pepper and Dijon mustard. Turn off heat and cover to keep warm.
Boil salted water and cook pasta al dente 10 to 12 minutes. Then drain pasta and add to cheese sauce. Stir in pasta and add to greased casserole dish. Top with bacon crumbles and grated cheese. Broil until melted. Finish with chopped scallions.
Recipe by Lowcountry Cuisine Magazine at http://lowcountrycuisinemag.com/recipes/mac-and-cheese-derek-falta-of-king-street-dispensary/