Preheat oven to 400˚ F. Spread the tomato halves out on a large baking sheet lined with foil, drizzle 2 T olive oil over the tomatoes and sprinkle generously with salt and pepper. Stir the tomatoes gently to coat them evenly. Roast the tomatoes for 45 minutes.

In a large stockpot, warm the 1 T of butter and 1 T of olive oil over medium heat until butter is melted. Add the onions and cook for about 10 minutes, until soft. Add the garlic and red pepper flakes and cook another minute. Add the remaining ingredients, stir, and bring the mixture to a boil. Lower the heat and simmer uncovered for 30 - 40 minutes.

Use an immersion blender or traditional blender to puree the soup until smooth (or leave it slightly chunky, which is what I prefer).