1. Preheat your oven to 350°F (175°C).
2. In a Dutch oven, heat a bit of oil over medium heat. Add the chopped onion and garlic, and cook until softened.
3. Add the carrots, celery, and mushrooms. Cook for about 5 minutes.
4. Stir in the tomato paste, thyme, rosemary, salt, and pepper. Cook for another 2 minutes.
5. Pour in the vegetable broth and add the chopped potatoes. Bring to a simmer.
6. Cover the Dutch oven and transfer it to the preheated oven. Cook for about 4 hours, or until the vegetables are tender.
7. Remove from the oven and let it sit for a few minutes before serving.