Alton Brown’s version is great, it’s available on Food Network website. 

No need to look it up. Here it is:
Alton Browns  Baked Macaroni and Cheese
Prep Time: 20 min     Cook Time: 45 min
Serves: 6 to 8 servings
Ingredients

[*]1/2 pound elbow macaroni [*]3 tablespoons butter [*]3 tablespoons flour [*]1 tablespoon powdered mustard [*]3 cups milk [*]1/2 cup yellow onion, finely diced [*]1 bay leaf [*]1/2 teaspoon paprika [*]1 large egg [*]12 ounces sharp cheddar, shredded [*]1 teaspoon kosher salt [*]Fresh black pepper

Topping:

[*]3 tablespoons butter

[*]1 cup panko bread crumbs

Directions
Preheat oven to 350 degrees F.
In a large pot of boiling, salted water cook the pasta to al dente.
While the pasta is cooking, in a separate pot, melt the butter. Whisk in the flour and mustard and keep it moving for about five minutes. Make sure it’s free of lumps. Stir in the milk, onion, bay leaf, and paprika. Simmer for ten minutes and remove the bay leaf.
Temper in the egg. Stir in 3/4 of the cheese. Season with salt and pepper. Fold the macaroni into the mix and pour into a 2-quart casserole dish. Top with remaining cheese.
Melt the butter in a saute pan and toss the bread crumbs to coat. Top the macaroni with the bread crumbs. Bake for 30 minutes. Remove from oven and rest for five minutes before serving.