1. Heat oven to 425 degrees F. In a rimmed baking sheet, liberally brush eggplant and tomatoes with oil; arrange eggplant cut side down and tomatoes cut side up. Brush cut side of garlic head with oil and wrap in foil. Roast vegetables and garlic until vegetables are tender and browning in spots, about 45 minutes. Let stand until eggplant is cool enough to handle, about 20 minutes; peel.
2. Meanwhile, in a large pot, heat oil over medium-low heat. Add onion and cook until softened, 10 to 12 minutes. Stir in tomato paste and cook 2 minutes. Add eggplant and tomatoes. Squeeze roasted garlic from skins into vegetables; stir to combine. Stir in broth, salt and pepper; bring to a simmer and cook 5 minutes. Puree using an immersion blender or a food processor. Makes 10 cups.