Grandma’s wartime recipe is this, but instead of ketchup you add canned concentrated tomato and equal amounts of water (just full the can once with water again, helps to get the last bit out) and that’s it. We call it red spaghetti, I make it for my kids from time to time, but this variation:

Grandma also added meatballs. Bake the small meatballs in a saucepan and when they’re done, do the tomato thing in that pan, stir well, then add to spaghetti. Can’t lose the grease, amirite…