Heat olive oil or butter in a large pot over medium heat. Add chopped onions, garlic, and celery. Cook until onions are soft and fragrant, about 5 minutes.

Stir in carrots and potatoes. Cook for another 3–4 minutes to blend flavors.

Add vegetable broth, just enough to cover vegetables. Bring to a boil, then reduce heat, cover, and simmer for 20–25 minutes or until vegetables are tender.

Use an immersion blender to puree the soup to your desired consistency. For a chunkier soup, blend only part of it.

Season with salt and pepper. Garnish with fresh parsley before serving, if desired.