Great Grammy'S Macaroni & Cheese - cooking recipe

Ingredients

1 lb elbow macaroni
2 tablespoons butter
3 tablespoons all-purpose flour
1/2 teaspoon ground mustard
1 pinch salt
1 1/2 cups whole milk, warmed
1/2 - 3/4 lb cheddar cheese, extra sharp, white, cubed
4 slices American cheese, white
1/2 cup parmesan cheese, grated, maybe more
ground black pepper

Preparation

Preheat oven to 350\u00b0F Grease casserole dish. Cook macaroni in boiling, well salted water until al dente. Drain.
Melt butter in top of double boiler. Add salt, ground mustard & flour, whick until smooth. Whisk in milk until smooth. Heat until thickened. *I will take the top of the double boiler & put it on direct heat BUT keep it low & do not stop stirring or it will burn & be ruined!*.
Add cheese & whisk until melted.
Put 1/2 cooked macaroni in casserole. Pour about 1/3 cheese sauce over macaroni. Stir well. Lay slices of American cheese over this. (4 slices fit my dish perfectly.) Add rest of macaroni & sauce. Stir carefully. Sprinkle top with Parmesan cheese to cover & some pepper to taste.
Bake 1 hour until top is browned & bubbly.