Below is the recipe that was shared above. I made this last night exactly as it is written and can confirm it is the truth. I used the HEB American Block cheese recommended above and shredded myself. If you brown the top a little longer, it would be very close to Chik-fil-a's.
This is a legit base macaroni and cheese that can now be used to play with other cheeses, bacon, green chiles, etc. The "dry milk roux" I think is the key. Enjoy, friends.
Luby’s Macaroni and Cheese
Ingredients
2 cups (8 ounces) dry elbow macaroni
4 tablespoons nonfat dry milk
2 tablespoons all-purpose flour
1 tablespoon butter or margarine, melted
1 ¼ cups boiling water
3 cups (12 ounces) shredded American cheese (found at deli counter)
¼ teaspoon kosher salt
To Prepare
Preheat oven to 350 F. Cook macaroni 1 to 2 minutes longer than package directions so pasta is soft but not mushy. Drain.
In a large mixing bowl, combine dry milk, flour, and butter. Whisking constantly, gradually add in boiling water. Add 1 cup of cheese and continue whisking until smooth and creamy, about 2-3 minutes.
Fold in macaroni, 1 more cup of cheese and salt.
Transfer to a lightly greased 11x7 inch casserole dish and cover with foil. Bake 25-30 minutes or until sauce in center of casserole is thick and creamy.
Remove foil and sprinkle remaining 1 cup of shredded cheese evenly over top. Return to oven until cheese melts.