Momma mac and cheese

Momma mac and cheese 1 large onion minced 1 stick butter 2 cans cream of mushroom soup 1/2 -2/3 cup of milk 1 pound very sharp cheddar cheese shredded 1 box of noodles of choice...I use elbow 1 can diced drained tomatoes sautee onion in butter til clear or done add soup cheese and milk stir almost constantly st keep from sticking cook noodles til done when cheese sauce and noodles are done mix in tomatoes pour into baking dish and bake for 10-15 min on 350 degrees until set.