Preheat the oven to 425°F.
Toss together the tomatoes, ¼ cup olive oil, salt, and pepper.
Spread the tomatoes in 1 layer on a baking sheet and roast for 35-40 minutes.
Heat 2 tablespoons of olive oil in a large stockpot over medium heat.
Add onions and red pepper flakes, and cook, stirring occasionally until the onions are translucent, about 10 minutes.
Add the garlic and sauté for 1 more minute.
Add the canned tomatoes, basil, rosemary and vegetable broth.
Transfer the oven-roasted tomatoes (and their liquid) into the stockpot.
Bring the mixture to a boil and simmer uncovered for 40 minutes.
Use an immersion blender or regular blender to blend the soup to a smooth consistency.
