Pioneer Woman's Stovetop Macraroni and Cheese

I keep seeing this over and over on different blogs. The pictures make me want to drool. Seriously. I usually eat mac and cheese out of a little box and the one time I made homemade macaroni and cheese it was not so creamy - but still good. This looked so creamy, that I knew the next one I'd try would be this one.

Ingredients
4 cups dried macaroni
1/4 cup butter
1/4 cup all-purpose flour
2 1/2 cups whole milk
2 heaping teaspoons dry mustard
1 egg, beaten
1 pound cheese, grated (I used half cheddar and half monterey jack)
1/2 teaspoon salt (more to taste)
1/2 teaspoon seasoned salt (more to taste)
1 teaspoon ground black pepper

Cook macaroni in a pot until done
Drain and set aside
In a large pot, melt butter and add flour in gradually
Stir together for five minutes
Pour in milk and mustard and stir until smooth
Cook until the sauce thickens
Reduce heat and stir in the egg until smooth
Add cheese and stir until melted
Add salt and pepper to taste.
Pour the macaroni into the sauce and stir to combine

Serve immediately

or you could top it with cheese and bake it, but really serve immediately.