Cook noodles according to package directions, with a bit of salt.
While they are cooking, brown ground beef, adding onions after a couple of minutes, after most of the beef is no longer pink. Cook, stirring, until beef is thoroughly cooked and onions have softened a bit. (Keep onions a bit firm; do not cook until translucent.)
Mix in tomato soup; stir well and heat for a minute or so, then stir in sour cream and heat another minute or so. Add drained hot noodles; stir thoroughly and enjoy!
Note: I have also added garlic, salt and pepper to this recipe (we love seasoning!), but my teens prefer this one best as written, without additional seasoning. Somehow it works, though it seems pretty plain, even to me :-).