Substitute Tomato Paste for Tomato Sauce
So, here's the thing: tomato paste is basically concentrated tomato sauce. To substitute it, you need to dilute it with some liquid, and the magic ratio is 1 part tomato paste to 2 parts water (or broth, or red wine, if you're feeling fancy). Mix it up, and voilà! You've got your tomato sauce substitute.
But, be warned: using tomato paste will give your dish a more intense flavor, so use it sparingly. You don't want your pasta sauce to taste like ketchup on steroids. Unless, of course, you're going for that old-school Italian vibe, in which case, go for it!