Creamy Mac n' Cheese

16 oz dry pasta (shells, rotini, radiatore)
1 egg, beaten
4 T butter
¼ C flour
2 ½ C milk
2 t (rounded) dry mustard
1 lb grated cheese (colby or cheddar)
½ - 1 t salt
½ - 1 t seasoned salt
¼ t black pepper
Optional: cayenne pepper, paprika, thyme

Cook pasta (undercook if baking, tender if serving immediately), drain, and set aside. In large skillet, melt butter over medium heat, then sprinkle in flour; whisk together for 1-2 minutes. Add mustard and whisk to combine. Pour in milk and whisk until thickened and smooth. Slowly add ¼ C of this mixture to beaten egg to temper it, whisking constantly, then whisk that mixture back into milk mixture. Add cheese a couple handfuls at a time and stir until melted. Add salts, pepper, and other seasonings as desired, then stir together with pasta. May serve immediately (creamy), or bake at 350 degrees for 25-30 minutes or until golden and bubbly. May top with crushed chips or cornflakes, if desired.