6 cups water
1 teaspoon salt
1/8 teaspoon vegetable oil
1 pound small elbow macaroni
2 tablespoons plus 1/2 teaspoon unsalted butter
2 tablespoons bleached all-purpose flour
2 1/2 cups milk
1/4 teaspoon freshly ground white pepper
1 teaspoon ground mustard
1/4 pound smoked Gouda cheese, grated (sometimes I do a combination of cheddar and Gouda)
Preheat the oven to 375 degrees F.
Put the water, 1/2 teaspoon of the salt, and the oil in a large, heavy saucepan over high heat and bring to a boil.
Add the macaroni and cook, stirring occasionally, until tender, about 8 minutes.
In a small, heavy saucepan, melt 2 tablespoons of the butter over medium heat.
Add the flour and cook, stirring constantly, for 2 minutes.
Slowly add the milk, whisking constantly.
Add the remaining 1/2 teaspoon salt, ground mustard, and the white pepper and continue whisking until the sauce is smooth and thick enough to coat the back of a wooden spoon, about 8 minutes.
Remove the white sauce from the heat and stir in the cheese. Continue stirring until the cheese melts.
Lightly grease a 6 1/2 by 10-inch casserole dish with the remaining 1/2 teaspoon butter. Combine the cheese sauce and macaroni in a large mixing bowl and mix well.
Pour into the prepared casserole and bake until lightly golden on top, about 20 minutes. Remove from the oven and serve hot.