4 cups dry macaroni
1 egg, beaten
1/4 cup butter
1/4 cup flour
2 1/2 cups whole milk
2 heaping teaspoons dry mustard (or more to taste)
1 lb. cheddar or other desired cheese, grated
1/2 tsp. salt (or more to taste)
1/2 teaspons seasoned salt (or more to taste)
1 tsp. ground black pepper
Cook the macaroni until very firm. The macaroni should be too firm to eat right out of the pot. (If you're in a hurry & don't want to bake the macaroni and cheese, cook it now until it's done.) Drain.
In a small bowl, beat the egg.
Preheat oven to 350 degrees F & butter a large oval or rectangular baking dish.
In a large pot, melt the butter & sprinkle in the flour.
Whisk it together over med-low heat. Cook for 5 minutes, whisking constantly. Don't let it burn.
Pour in the milk.
Add the mustard & whisk until smooth. Cook for 5 minutes or until very think, whisking constantly. Reduce the heat to low.
To temper the egg, slowly pour 1/4 cup of the sauce into the beaten egg, whisking constantly to avoid cooking the egg. Whisk until smooth.
pour the egg mixture into the sauce, whisking until smooth.
Add in all but 1/2 cup of the cheese & stir until melted.
Add the seasonings. Taste the sauce & add more as needed. Do not undersalt or you'll regret it the rest of your life!
Pour in the cooked, drained macaroni & stir to combine.
Serve immediately or pour into the baking dish & top w/the remaining cheese.
Bake for 20-25 minutes, or until bubbly & golden on top.