Roast the Roma tomatoes at 375°F for 1 hour with olive oil, salt, and pepper.
Sauté the onion in oil/butter for about 5 minutes.
Add garlic, thyme, salt, and pepper and sauté another minute.
Add crushed San Marzano tomatoes, basil, and sugar. Simmer for 10 minutes.
Add chicken stock and roasted tomatoes. Simmer another 30 minutes.
Blend until smooth or to your preferred texture, preferably with an immersion blender.
Stir in the heavy cream and serve with homemade sourdough croutons, crackers, sourdough bread, French bread, or sourdough garlic toast.