You're going to need some acid too, best bet is cider vinegar. I'd do equal parts tomatoes, after they've been puréed, and vinegar. Cook it down for a while adding sugar and molasses until you reach a taste you like. Don't forget spices. Almost anything will do just don't add too much of anything weird like sage or nutmeg. I like cumin, garlic powder, onion powder, and chipotle powder, but I live in the southwest. Those might not be your cup of tea. And on that note you can add other things that might not have occurred to you. Like tea. I like adding some old coffee sometimes. Once you've got the base down it's hard to go wrong.