Preheat the oven to 220C; in a bowl mix the tomatoes with salt, pepper and a generous glug of olive oil; spread evenly on a baking tray and bake for 40 minutes; while the tomatoes are baking met the butter with some olive oil; sauté the onion, garlic and chili flakes (if using) until the onions have browned; Add the can of tomatoes, herbs, vegetable stock and the roasted tomatoes; bring to boil and reduce to a simmer; Simmer for 40minutes; Puree the soup and season to taste; serve hot.