Saute onion in 1 tablespoon butter until it is transparent. Let the onion cool slightly. Put the slices of bread in a mixing bowl and pour milk over them to soak for a minute. Put onion, meat, egg and seasonings in the mixing bowl with the onion and blend thoroughly using your hands. Shape the mix into 1.25" (1 1/4 inch) balls and roll them in dry bread crumbs. Brown the meatballs slowly in the remaining 2 tablespoons of butter. Drain off all but 2 tablespoons of fat. Pour in tomato sauce and simmer for 20 minutes.

In a separate pot, bring salted water to a boil and cook the spaghetti noodles as directed via the box. (I usually use wheat noodles)