• Preheat oven to 350 degrees.
• Lightly spray a Large Deep Casserole Dish with cooking spray, set aside.
• Boil 4 quarts of salted water, then add noodles. Wait for re-boil, gently boil noodles uncovered for approx. 8 minutes (you want them to be al-dente) Drain noodles; pour into greased casserole dish

Make cheese sauce

• Melt butter in a large pot on medium.
• Add flour & mustard, stir constantly, until smooth and starts to turn tan in color. This will takee a few minutes
• Slowly add heavy cream, a quarter cup at a time, mix constantly until incorporated until adding more. Once all the cream is added, continue to mix until thickened (this can take 5 minutes or so)
• Add 4 cups cheese, stir with until completely melted.

Finish the dish

• Pour the (drained) noodles into the baking dish. Pour cheese sauce over noodles, mix well. Top with additional cheese.
• Cover; bake 45 minutes. Uncover; bake 15 minutes longer.