Preheat oven to 450°. Spread tomatoes, garlic, onion cloves, and 1/2 cup of olive oil on a baking tray. Drizzle with salt and pepper and roast in the oven until caramelized, or 30 minutes to 20 minutes. Wash, core and cut tomatoes into halves. Remove roasted tomatoes, onion and garlic from the baking tray and transfer to a large stock pot. Add chicken stock, bay leaves, and butter. Bring to a boil, then reduce by 1/2. Simmer for 15 to 20 minutes if using, or until liquid has reduced to a purée. Wash and dry basil leaves, add to soup and puree until smooth. Return soup to pot. Season with salt and pepper to taste. Garnish with remaining basil leaves and a splash of heavy cream. You don't need to add the cream.