I've been making this dish since the early 60's and my mother made it before me, but never with pre-cooked macaroni or onion salt. The original Mom's Monday macaroni was a dish most often made on washday Monday, as doing the wash in the 50s -60's was an all day chore if you weren't fortunate enough to have a fancy wringer washing machine. The recipe I made a lot when my children were young, and still do make occassionally for my DH and I is, 1 tablespoon butter, 1 small onion finely chopped, 1 1/2 cups Uncooked macaroni, 1-2 cups cups of cubed cheddar cheese, 1 can tomatoes, (19 oz) undrained, (chop them up if whole) 1 cup water, 1 teaspoon salt, pepper to taste. Topping: 1 teaspoon soft butter, 1/2 cup soda cracker crumbs, (about 8 crackers).
In skillet over medium heat, melt butter. Add onion and saute for 4 min or til onion is limp (if you're pressed for time or feeling particularly lazy, you can skip this and just toss in the raw onion). Grease a casserole dish with lid and add macaroni, cheese, tomatoes, water, salt and pepper. Stir in onion mixture and stir well to break up tomatoes. Bake covered in a 350 oven for 30 min.
TOPPING: combine butter and cracker crumbs (you can use dry bread crumbs or crushed cornflakes, etc.) season with salt and pepper. Sprinkle topping evenly over top. Return to oven and bake, UNCOVERED, for 20 min. longer or til crumbs begin to brown and macaroni is tender.
Serves 4 - 6 depending on appetites.