Preheat oven to 400 degrees F (200C). Place the quartered tomatoes, and onions on a baking sheet. Drizzle tomatoes and onions with olive oil. Generously season with kosher salt and freshly ground pepper. Cut top off of a head of garlic and place it on a sheet of aluminum foil. Drizzle the top of the garlic with olive oil and wrap it up tight and place on baking sheet. Roast for 40-45 minutes.
Once the tomatoes, onions, and garlic are done roasting, allow them to cool for 10 minutes, then add them to a stock pot on the stove and use an immersion blender to blend until smooth. Next add the basil and blend again.
After blending, turn stove on to medium heat and add in oregano, broth and salt and pepper to taste. From there you can add in any additional add-ins if desired (listed in the ingredients). Allow soup to simmer for 10 minutes before serving.
