Start by making your soup: Add olive oil to a pot. Once warm add the onion and salt. Cook on low heat for 10 minutes, stirring occasionally to make sure it doesn't burn.
Step: 2
Add the tomato paste, mix it in, and cook for 30 seconds more.
Step: 3
Add the canned tomatoes and vegetable broth. Increase the heat, bring the mixture to a gentle simmer and cook for 30 minutes, while stirring occasionally. Don't bring it to a boil, maintain a gentle simmer throughout the 30 minutes.