This is one of my favorite dishes, shrimp and crab in a Mornay sauce served over broccoli and egg noodles.
This starts with butter and flour in a roux. Cook it for a bit and then stir in some milk. As the milk comes to a simmer it will thicken and smooth out. Keep it at a simmer for a few minutes while constantly stirring then stir in a few ounces of cheese. Today I used some Swiss cheese and Parmesan. I grated a bit of nutmeg into it, that is strictly optional.
The crab was precooked so I folded it into the sauce. The shrimp I steamed for a few minutes and combined them with some steamed broccoli in a greased casserole and then poured the cheese mixture atop that. Topped the cheese with some herbed bread crumbs and set the dish in a 350 oven until it bubbled and browned a bit.
I like the egg noodles with this, I imagine any kind of pasta would work, as would potatoes, or a rice preparation of some kind.