4 lb tomatoes, halved lengthwise
6-8 garlic cloves, left unpeeled
3 tablespoons olive oil
1/2 teaspoon salt
1/4 teaspoon black pepper
1 medium onion, finely chopped
2 teaspoons fresh oregano, minced [use only 1/2 tsp if you used dried]
2 tablespoons fresh basil, minced [use only 1 tsp if using dried basil]
2 teaspoons sugar
2 tablespoons unsalted butter
3 cups chicken stock or low-sodium broth
3/4 cup heavy cream
Put oven rack in middle position and preheat to 350°F.
Arrange tomatoes, cut sides up, in 1 layer in a large shallow baking pan and add garlic to pan. Drizzle tomatoes with oil and sprinkle with salt and pepper. Roast tomatoes and garlic 1 hour, then cool in pan on a rack. Peel garlic.
Cook onion, oregano, basil, and sugar in butter in a 6- to 8-quart heavy pot over moderately low heat, stirring frequently, until onion is softened, about 5 minutes. Add tomatoes, garlic, and stock and simmer, covered, 20 minutes.
Purée soup in batches in a blender (use caution when blending hot liquids), then force through a sieve into cleaned pot, discarding solids. Stir in cream and salt and pepper to taste and simmer 2 minutes.
Divide soup among 8 bowls.