Homemade Mac and Cheese with Ham

2 quarts water
2 tsp salt
1 tbsp oil
1 3/4 c macaroni
2 c diced cooked ham
1 1/2 c grated cheddar cheese (divide into 1 c and 1/2 c)
2 tbsp margarine or butter
1/4 c flour
1/2 tsp salt
1/4 dry mustard
2 1/2 c milk
1/2 c crushed potato chips

Heat oven to 350 deg. Boil water in large deep pot with 2 tsp salt and oil (to prevent boiling over). Add macaroni. Cook uncovered after water returns to a boil for 10-11 min. Stir occasionally. Drain and rinse under hot water. In 2 quart casserole dish, combine cooked macaroni, ham, and 1 c cheese. In medium saucepan, melt margarine. Blend in flour, 1/2 tsp salt and mustard. Add milk all at once. Cook until thickened, stirring constantly, about 1 min. Combine sauce with macaroni mixture. Toss 1/2 c cheddar cheese with potato chips. Sprinkle over top. Bake at 350 deg for 25-30 min.