Preheat the oven to 350°F.
Line four baking sheets with aluminum foil and brush them with half of the olive oil.
Place the tomatoes in the baking sheets and sprinkle the garlic.
Drizzle with olive oil, salt and pepper.
Roast the tomatoes for 1 hour.
In the meantime, in a pot over medium heat, heat the rest of the olive oil and the butter.
Sauté the onions and the thyme until soft, about 5 minutes.
Add the roasted tomatoes and the water, and cook for 20 minutes.
Discard the thyme sprigs.
With an immersion blender, blend all the ingredients until they become a pretty smooth soup.
Season with salt and pepper.
Garnish with goat cheese and a sprig of thyme.