Place tomatoes on a non-stick baking sheet. Sprinkle with fresh thyme and garlic. Sprinkle with salt and pepper and drizzle with two tablespoons of the olive oil. Bake tomatoes for about 2 hours, until the skins shrivel and they are slightly dried.
While tomatoes are slowly roasting and almost done, heat the remaining olive oil in a stockpot and saute the onion about five minutes until tender. Place roasted tomatoes and onion in a blender and gently puree (mixture does not have to be completely smooth). Return pureed mixture to stock pot, add chicken stock and simmer 5 to 10 minutes.
Garnish with grated cheese and your favorite croutons.