Okay, this is my best mac-n-cheese recipe. I pretty much stole it from a show on the food network ...working from memory and trying to scale for 15...
It sounds a lot more complicated than it is. As long as you get all the cheese grated/crumbled first, it's quite easy.
2 16-oz packages macaroni elbows (or whatever pasta you want to use; I'd probably use mini-penne)
1/2 pound bacon, diced.
1 large onion, diced.
1 stick butter plus a little extra
1/4 to 1/3 cup flour
1 tablespoon Dijon mustard.
4-5 cups whole milk
4 cups whipping cream (aka "heavy cream")
several sprigs fresh thyme (or 1/2 teaspoon dried)
two bay leafs (optional)
3/4 teaspoon salt
1/4 teaspoon coarse ground pepper
Cheese:
Fontina: 2 1/2 cups.
Gruyere: 1 1/2 cups.
Sharp or extra sharp cheddar (think Vermont here, not Kraft): 1 1/2 cups
Blue (yes, this is essential; Danish or Maytag is fine): 1/2 cup.
Parmesan (fresh grated P. Reggiano is best, but anything other than the powdered kind):: 1 1/2 cups
Velvetta (yes, this is essential, too). 1 1/2 cups
Chopped flat-leaf (Italian) parsley.
Bread crumbs (optional)
Butter your baking dishes. Don't know what you have in this regard, but if I'm cooking for 15, I'd do it in two 9x13 dishes. Preheat oven to 450.
Cook macaroni and drain. Don't overcook, a little extra al dente is better than soggy. Then:
1.In big pot/dutch oven: saute bacon until crisp. Remove bacon and set aside. Drain most of grease as well (leave maybe a strong tablespoon).
2. Add onion and saute until softened. Add butter and melt. Whisk in flour until you have a light brown roux. Whisk in mustard.
3. Add milk and cream, slowly. Whisk constantly.
4. Add thyme, bay leaf, salt and pepper. Lower heat and simmer about 10-15 minutes. Stir often.
5. Reserve about 1/4 cup each of cheddar, fontina, gruyere, and parmesan Stir in rest of cheeses, crisp bacon, and parsley. Some would remove from heat entirely here, but it always takes me longer to get the cheese all melted where I like it, so I leave it on low heat for part of the stir-in.
6. Once all the cheese is mixed, stir in pasta.
7. Put it all in the baking dish(es). Mix together bread crumbs and reserved cheeses, sprinkle on top.
8. Bake about 15-25 minutes until bubbling/golden brown on top.
And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.
Romans 12:2 (NKJV)