Preheat oven to 375 degrees F. Prepare baking tray. Spread tomatoes, onion and one head of garlic. Roast for 20 minutes. I usually always have roasted garlic in my fridge, as the garlic usually bakes for 40 minutes.
Add the roasted tomatoes, onion and squeeze the roasted garlic into your vitamix. Blend smooth. Pour through a sieve for a smooth, creamy soup.
Transfer to pot and reheat, add basil, fresh is best, and salt and pepper to taste.