Macaroni and Cheese

4 cups dried macaroni
1/4 cup (1/2 stick) butter
1/4 cup all-purpose flour
2 1/2 cups whole milk
2 heaping teaspoons dry mustard
1 egg beaten
1 pound (sharp) cheese, grated
1/2 teaspoon salt
1/2 teaspoon seasoned salt
1 teaspoon ground black pepper
Optional spices: cayenne pepper, paprika, thyme

Preheat oven to 350.
Cook macaroni until very firm. Macaroni should be too firm to eat right out of the pot. Drain.
In a large pot, melt butter and sprinkle flour. Whisk together over medium-low heat. Cook mixture for five minutes, whisking constantly. Don't let it burn. Pour in milk, add mustard, and whisk until smooth. Cook for five minutes until thick. Reduce heat to low.
Take 1/4 cup of sauce and slowly pour into beaten egg, whisking constantly to avoid cooking eggs. Whisk together until smooth. Pour egg mixture into sauce, whisking constantly. Stir until smooth. Add in cheese and stir to melt. Add salts and pepper. Taste sauce and add more salt and seasoned salt as needed.
Pour in drained, cooked macaroni and stir to combine.
Serve immediately (very creamy) or pour into a buttered baking dish, top with extra cheese, and bake for 20-25 minutes or until bubbly and golden on top.

Source: Pioneer Woman