This is not your out of the box Mac 'N Cheese. Heck, I doubt you could even get this delicious, creamy, cheesy blend in any restaurant.
Preheat oven to 350º
Slice slab bacon into ½" cubes. Chop onion, grate cheese, peel garlic. Bring a pot of salted water to a boil and add macaroni. Boil macaroni until it is al dente, then put aside. Cut broccoli into bite size pieces. Steam until sweating and just off crunchy. Put aside. Mix parmesan cheese and panko bread crumbs in a bowl and set aside.
If your bacon is very lean, add a tablespoon of oil to dutch oven. Add bacon, onions, mince in the garlic, smoked paprika, and dry yellow mustard to the dutch oven. Brown until bacon Is cooked through and the onions are clarified.
Combine bacon, macaroni, and broccoli in the dutch oven. Prepare the cheese sauce and pour it into the dutch oven. Stir until everything is evenly coated with cheese sauce. IF it seems a little too sticky, add another cup of cream and stir. Sprinkle the panko bread crumbs and cheese mixture over the top of the casserole.
Bake, uncovered, for about 30 minutes at 350ºF. If the top isn't browned after 30 minutes, cook under the broiler for 3 or 4 minutes, or until browned.
In a large saucepan, melt the butter. Add the flour and cook until the colour changes to a light brown.
Gradually add the cream, bring to a boil, stirring constantly. Once the béchamel is creamy, add the sour cream, cayenne, and nutmeg. Keep stirring.
Turn the heat down to medium. Add the grated cheese a little at a time whisking constantly. The sauce should be creamy and smooth.
If you don't have a dutch oven, fry the bacon and onions in a frying pan. Build the casserole, except for the topping, in a large bowl. Portion the mixture into casserole dishes, top with the topping and bake at 350º for 30 minutes.