Tomato soup and tomato sauce seem like very different recipes, but they're not as dissimilar as you think. You might even be able to use one to make the other.
Once you get the hang of making basic tomato sauce, you can improvise by adding ... 1 can (400 grams) canned tomato, 1/8 (20 grams) onion, 1 clove garlic, 3 Tbsp olive oil, 1/2 tsp dried oregano ...