In a large pot, melt butter over medium heat. Add onion, carrots, and celery, and cook until softened, about 5 minutes. Stir in garlic, thyme, and oregano, and cook for another minute.
Gradually add vegetable broth while stirring continuously to avoid lumps. Add potatoes and bring to a boil. Reduce the heat and simmer until potatoes are tender, about 15 minutes.