- In a large pot, heat olive oil over medium heat. Add onions, carrots, and celery. Cook until slightly softened, about 5 minutes. 
- Stir in garlic and ground beef. Cook until beef is browned and cooked through. Drain excess fat if needed. 
- Add diced potatoes, chicken broth, salt, and pepper. Bring to a boil, then reduce heat and simmer for 15-20 minutes, or until potatoes are tender. 
- In a separate bowl, whisk together milk and flour (if using) and add to the pot. Stir well and cook for 5 more minutes to thicken. 
- Stir in shredded cheddar cheese and sour cream until melted and smooth. 
- Taste and adjust seasoning. Serve hot with extra cheese or green onions, if you're feeling fancy.