In a large soup kettle, heat olive oil. Once hot, add onions and celery. Saute over medium heat until soft, about 10 minutes.
Once soft, add potatoes, garlic, and chicken stock. Raise to medium-high temperature and bring to a boil.
Cook until the potatoes are soft, 10-15 minutes.
Once soft, remove 2-3 cups of the mixture and blend with a stick blender until smooth.
The amount is dependent on how creamy or brothy you want your soup.
Stir smooth vegetables back into the soup with milk, pepper, thyme, and rosemary.
Allow to simmer over low heat for an additional 5-10 minutes.