Generously season the ground beef with salt and pepper. In a large stockpot over medium heat, brown the beef, breaking it apart into fine crumbles with a wooden spoon or meat chopper. Once fully browned, remove the beef with a slotted spoon and set aside on a plate.

Introduce the olive oil into the same pot, followed by the onion, celery, carrots, and garlic. Sprinkle in a substantial pinch of salt and pepper, along with the oregano. Sauté this mixture, stirring regularly, until the vegetables are tender, about 5 to 6 minutes.

Stir in the quartered potatoes and pour in 4 cups of chicken stock. Return the browned beef to the pot, bring the contents to a boil, then lower to a simmer and cover. Cook for approximately 10 to 15 minutes, or until the potatoes are fork-tender.

In a separate skillet, melt the butter over medium heat. Add the flour and whisk continuously for 2 to 3 minutes to create a roux, until the mixture turns golden and emits a nutty aroma.

Carefully incorporate the roux into the soup pot using a spatula. Raise the heat and bring the soup back to a boil for 1 to 2 minutes. Stir in the milk and cook for an additional 1 to 2 minutes.

Lower the heat to a gentle simmer and mix in the shredded cheddar cheese, stirring until completely melted. If a thinner consistency is preferred, introduce the remaining cup of chicken stock. Taste and adjust the seasoning with additional salt and pepper if needed.

Finally, blend in the sour cream until smooth and fully incorporated. Serve hot, garnished with a sprinkle of fresh