Out of tomato paste? For 1 tablespoon, simmer 3 tablespoons tomato sauce in a small pan until it darkens and holds on a spoon.
1 tbsp tomato paste = 3 tbsp tomato sauce (simmer to reduce)
Good for soups, stews and pasta sauces. Stir often. The time it takes depends on how thick your sauce is, so watch the pan.