Cook the noodles in a large pot of boiling salted water. Slightly undercook the noodles until they are al dente, meaning that the pasta is tender but still firm to the bite. Drain noodles in a colander, and then run noodles under cold water to halt the cooking. Drain well, and set aside.
Meanwhile, make the béchamel sauce. In a medium-sized pot, add the oil and flour, and heat over medium high heat. Whisk until the flour is incorporated, and cook for a few minutes. Gradually add in the milk and whisk until the sauce is smooth and thickens up, about 5 minutes. Turn heat to low, and stir in the shredded cheese. Add nutmeg, salt, and pepper. Taste and adjust seasonings.
To make ahead, put the noodles in a large casserole, and pour the sauce over the noodles. Gently, fold the noodles over to coat the noodles in sauce. The dish will be extra saucy now, but will be just right when reheated.
Let the dish cool, then cover and refrigerate.
Let the mac and cheese sit out at least 30 minutes before putting it in the oven so that the casserole dish will not break from heat shock. When ready to serve, preheat the oven to 375°F. Heat the mac and cheese covered for about 30 minutes or until dish is warm and sauce is bubbling, then serve.
If serving immediately, make the following adjustments: do not run cold water over the cooked pasta, use about ¾ of the cheese sauce, and no need to bake it.
Using lactose free milk and aged cheddar will make this a lower lactose recipe. Aged cheddar usually has less lactose.
Don’t put a cold dish into a hot oven or it may break. Let the macaroni sit out at room temperature after removing it from the refrigerator about 30 minutes before putting it in the oven.
How to store: Store the unbaked macaroni and cheese covered in the refrigerator for 1-2 days. Once baked, keep leftovers in the refrigerator in an airtight container for 3-4 days.
How to freeze: Freeze baked macaroni and cheese in a freezer safe container for up to 6 months.
How to reheat: Let the casserole dish sit out for about 30 minutes at room temperature. Add to a 375°F oven to reheat until warmed throughout.