6oz tomato paste
1 cup water
1 tbsp sugar
1 tbsp oil
1 tsp salt
1/4 cup vinegar
Bring to a boil then leave on low heat for a couple hours.
Unfortunately I don't think my notion of "low heat" was low enough, since it burned on the bottom real bad after about an hour. The goop left on top was actually pretty ketchup-like in consistency, but the flavor was way too tomatoey-sweet. I think I should increase salt and vinegar and decrease sugar and maybe eliminate oil.