Add butter to your saucepan and allow it to start melting over medium-high heat. Add your onion, celery, and carrot (see note) and cook until the onions are thoroughly cooked down. You would like to see a fond beginning to form on the bottom of the pan (the pan starts to turn brown but not burnt/black). This is flavor and you want to have a lot of it.
Add tomato juice to deglaze the pan. Add vegeta. Add additional water.
Bring the soup to a boil then reduce to a simmer. Cover and boil for at least 30 minutes.
While the soup is simmering, remove 1-2 ladles of soup and place in a small bowl/cup. Whisk in sour cream. Pour the mixture back into the soup and stir.
Add the noodles and cook for an additional 15-20 minutes.
Taste the soup, add additional water, salt, and pepper as necessary. Add a dash of magi if desired.