Cook noodles according to package directions. Drain. Melt margarine over medium-low heat. Stir in cornstarch. Gradually add milk, stirring constantly. Bring to a boil while still stirring constantly so it doesn't scorch. Add cheese. Stir in cooked noodles and salt.
I made this and then added a thin layer of shredded cheese and stuck it in the oven at 350 for about 10-15 minutes. It made the top nice and crunchy and give extra texture. I'm sure breadcrumbs would work as well.