In a large pot over medium heat, cook and crumble 1 pound of ground beef for 6-8 minutes, stirring occasionally until browned and cooked through. Drain excess fat.

In the same pot, melt 2 tablespoons of butter over medium heat. Add 3/4 cup diced carrots, 3/4 cup diced celery, and 3/4 cup diced onion. Sauté for about 10 minutes until tender.

Stir in 4 cups of diced potatoes and 3 cups of chicken broth. Bring to a boil, then reduce heat and simmer for 10-12 minutes until potatoes are fork-tender.

In a separate saucepan, melt 2 tablespoons of remaining butter over medium heat and whisk in 1/4 cup of flour. Cook for 3-5 minutes until bubbling and light golden.

Reduce heat on the soup pot. Gradually stir in the roux until thickened. Add 1 to 2 cups of cubed Velveeta, 1.5 cups of whole milk, salt, and black pepper. Stir until cheese is melted.

Remove from heat and stir in 1/4 cup of sour cream until well combined.

Serve hot in bowls, topping with optional ingredients like onion rings, green onions, or bacon.