Preheat oven to 450℉
Line a rimmed baking sheet with parchment paper. Wash and core the tomatoes, cutting out any bad spots, halve or quarter them (depending on their size), and spread them with the garlic and onions on the baking sheet. Drizzle with olive oil and sprinkle with salt and pepper.
Roast for 30-40 minutes until the tomatoes start to carmelize.
Remove from the oven and add to a large stockpot with the stock, bay leaves, and red pepper flakes. Bring to a boil and simmer for 20-30 minutes until the soup has reduced by about 1/3. Add salt/pepper to taste.
Remove the bay leaves and blend with an immersion blender, or add in parts to a blender (be careful not to overfill or your blender will blow its top and you could get seriously burned, not to mention the mess!)Garnish with additional fresh basil leaves, croutons, or anything you like!