Homemade Macaroni N Cheese

4 c elbow macaroni
4 TBS margarine
1/4 c all-purpose flour
2 1/2 c milk
2 tsp (heaping) dry mustard
1 egg, beaten
1 lb shredded cheddar cheese
1/2 tsp salt
1/2 tsp seasoned salt (Lawry's works best)
1/2 tsp black pepper
cayenne pepper, paprika & thyme for sprinkling

Cook macaroni in boiling water for ONLY 5 minutes. It should be too firm to eat out of the pan (this is the secret for it not overcooking when you bake it I learned); drain. Preheat oven to 350F. While that is boiling/cooking, put egg in a small bowl and beat it with a whisk. In a large pot (NOT the one you are cooking the pasta in), melt butter and sprinkle in flour. Whisk together over low-medium heat whisking constantly so as not to let it burn. When it is mixed together pour in milk and put in dry mustard and whisk until smooth. Cook until it is thick and then reduce heat to low. Take 1/4 c of the sauce and slowly pour it into the beaten egg, whisking constantly to avoid cooking the egg. Whisk together until it is smooth. Pour egg mixture into sauce whisking constantly. Stir until smooth. Add in all but 1/2 c of the cheese into the pan and stir until the cheese is melted. Turn off the heat, add all the seasonings, stir one last time, and then pour the drained macaroni into the cheese mixture. Then, pour mixture into a greased 9x13 pan; sprinkle remaining cheese on top (I used even more than the 1/2 c because I wanted it covered in cheese, the cheese you sprinkle over it is going to become a crispy top, which is the secret to the creamy, soft bottom). Bake for 20 minutes or until the top is bubbly and golden brown.