How do I substitute tomato paste for tomato sauce?
I often make changes like that, primarily because you get a better-quality product when you do. Try using 1/2 water (or stock if you have any) and 1/2 tomato paste. Add a little Italian seasoning, i.e. basil, oregano, garlic, parsley and a bit of sugar. Start with 1/4 tsp. of each, taste your concoction and go from there. Most recipes are not so finicky that they would suffer from such a change, and the bonus is that there are no unpronounceable ingredients in your sauce. Good luck!
Tomato paste can be used by adding 2 cans of water. (6 ounce can, 12 ounces of water) This will make it have a more sauce like quality. It is not salted or seasoned. I add 1 tablespoon each of dried parsley, basil and oregano, 1 teaspoon each of salt and garlic powder. This is when I am making spaghetti sauce. When I am making chili, I just add it to the beans that already have the liquid in them. You really can add it to anything that you want to have a tomato flavor. Add small amounts of water until you get the consistency you want.
Most tomato sauce is loaded with salt. Your starting idea (paste +water+ ?) offers an alternate choice. Try 1 1/2 water to paste (9 oz water to 6 oz paste) and add water for a thinner sauce. Then add Italian spices (basil, oregano, marjoram, parsley) a little at a time while tasting.
If you add raw garlic and or onion, try cooking them lightly in olive oil first to mild them down. Garlic powder and onion powder (both come in low-sodium versions) are options. All ideas are optional, including yours. Enjoy, pc