In a large pot or Dutch oven, brown the ground beef over medium-high heat. Drain off any excess fat.
Add the chopped onion and celery to the pot and cook until softened, about 5 minutes.
Stir in the diced potatoes and chicken broth. Bring to a boil, then reduce heat and simmer for 20 minutes, or until the potatoes are tender.
In a small bowl, whisk together the flour and 0.25 cup cold water to form a slurry. Gradually whisk the slurry into the soup and simmer for 5 minutes, or until slightly thickened.
Stir in the heavy cream (if using) and season with salt, pepper, and parsley to taste. Heat through, but do not boil.
Serve hot and enjoy!
Notes
This soup is even better the next day! Store leftovers in an airtight container in the refrigerator.