4 tablespoons Butter or margarine
Melt the butter in a saucepan. Stir in the flour, and cook briefly until the mixture looks sandy. Do NOT let it color. Whisk in the half-and-half, and stir until the mixture forms a thick sauce. Stir in the cheese, and season to taste. Simmer for a few minutes to blend the flavors, and stir in the crab meat. Cook JUST until the crab is heated through. Serve over cooked linguini, with additional Parmesan cheese and hot red pepper flakes on the side.
Before some purist jumps me, I KNOW this isn't a classic Alfredo, but it is a very good dish, and remarkably easy to make. Also, the sauce is purposely thick because I like it that way =P, just add more liquid ingredient if you want it thinned!
This may be varied by substituting cooked lobster meat for the crab, or by adding 36 cooked, peeled and deveined medium shrimp, and about a quarter of a cup of chopped cooked broccoli instead of the crab meat.