Clean the peppers from their seeds and cut them into quarters.
Cut the tomatoes in half. In a tray covered with foil, place the peppers, tomatoes and garlic cloves. Sprinkle with oil and bake in an oven heated to 446°F (230 °C) for around 25-30 minutes until ready.
Clean the roasted vegetables from their skins and transfer them to a blender. Bring the broth to a boil.
Put the blended vegetables in the broth.