Prepare the Vegetables: Peel and dice the potatoes, carrots, and celery. Dice the onion and mince the garlic.
Heat the Olive Oil: In a large pot or Dutch oven, heat the olive oil over medium heat.
Sauté the Aromatics: Add the diced onion and cook until translucent, about 5 minutes. Add the minced garlic and cook for another minute.
Add Vegetables: Stir in the diced potatoes, carrots, and celery. Cook for about 5 minutes, stirring occasionally.
Add Broth and Herbs: Pour in the vegetable broth, and add the dried thyme and rosemary. Bring to a boil.
Simmer: Reduce the heat and let the soup simmer for about 20-25 minutes, or until the vegetables are tender.
Blend the Soup: For a creamier texture, use an immersion blender to blend the soup until smooth. Alternatively, transfer the soup to a blender in batches and blend until smooth, then return to the pot.
Add Milk: Stir in the milk and heat through without boiling. Season with salt and pepper to taste.
Serve: Ladle the soup into bowls and garnish with fresh parsley if desired. Serve hot.