Preheat the oven to 232 degree celsius.
Wash and cut the tomatoes into halves and remove the seeds.To save additional juice, you can strain the seeds and tomato pulp into a bowl. Keep it aside.
Take two baking sheets and spread the onions, tomatoes, add garlic cloves on top of it. Next drizzle the olive oil on top of it and season it with salt and pepper.
Roast these vegetables for 25 minutes till they are caramelized.
Take a large pot/pan, put in the roasted vegetables and pour in the kept aside tomato juice along with the stock.
Bring this mixture to a boil then reduce the flame. Let this simmer and cook for 30 minutes or so till the liquid reduces by a third.
Wash and pat dry the basil leaves, then put them into the pot. Switch off heat and let soup cool down for 10-15 minutes. Then, pour this soup into a grinder and blend till it is smooth.
After this, pour the soup back into the pan and adjust the seasoning of salt and pepper according to taste. Let it simmer for 5-6 minutes.
Serve warm with a side of soupsticks/crustybread.