Simple but Elegant Macaroni and Cheese

1 cup diced onion

1-2 cloves finely chopped garlic
2 tablespoons unsalted butter
2 tablespoons unbleached all-purpose flour
2 cups low-fat milk
1 tablespoon Dijon mustard
10 ounces extra-sharp aged white Cheddar, grated, plus 2 ounces, grated (see Help Note)
Salt and freshly ground pepper to taste
1/8 teaspoon ground nutmeg
1/4 to 1/2 teaspoon hot pepper sauce
1 box cavatappi
Grated Parmigiano-Reggiano to top

(saute onion in butter, add garlic and saute a few min more, then make a roux by adding equal parts flour to the butter and stir until lightly golden; whisk in milk or fat free half and half until creamy; add mustard, spices, and shredded cheese, and stir to incorporate. can also use garlic and onion powder as a shortcut)

1. In a large saucepan, cook the onion over low heat in the melted butter until the onion is soft but not browned, 5 to 7 minutes. Stir in the flour. Remove from the heat and whisk in the milk until thoroughly blended. Return to medium heat and cook, stirring, until the mixture begins to thicken. Remove from the heat and stir in the mustard and the 10 ounces of Cheddar, the salt, pepper, nutmeg, and hot pepper sauce.
2. Meanwhile, cook the cavatappi according to package directions until just al dente. Drain but do not rinse; save a few tbsp of pasta liquid to add to bechemel. Stir immediately into the prepared cheese sauce until well blended. Adjust the seasonings.
3. Spoon the mixture into a 9 by 13-inch baking dish. Top with the remaining 2 ounces of Cheddar and the Parmigiano-Reggiano.
4. Place the rack in the bottom third of oven. Preheat the oven to 400 degrees and bake for about 30 minutes, until the mixture is hot, bubbling throughout, and golden.
Help Note: The finished casserole can be refrigerated before baking. To serve, let the dish return to room temperature and follow the directions in step 4.
The quality and sharpness of the cheese are important; use a white Cheddar that has been aged at least 2 years.
Other corkscrew pastas can be substituted for the cavatappi; the sauce adheres beautifully to this shape.

for variation, try adding more heat (cayenne), a drizzle of truffle oil over the top, fresh chunk lobster, sage and spicy sausage, or use some smoked gouda, gruyere, or mixture of cheeses.

i made this dish a 'seafood mac' by adding chunk lobster, bay scallops, and smoked salmon with a mixture of gruyere, aged white cheddar, and a bit of smoked cheddar cheese, topped with parmesean.