Combine the ground beef, one tablespoon of butter, and the Montreal seasoning in a large soup pot over medium-high heat.
Sear the beef until it reaches a deep brown crust, then remove from the pot and set aside.
In the same pot, add the remaining butter and sauté the onions and celery until softened.
Stir in the minced garlic and cook for 1 minute until fragrant.
Sprinkle the flour over the vegetables and stir constantly for 1-2 minutes to create a roux.
Slowly whisk in the milk and beef stock, ensuring no lumps remain.
Add the diced potatoes and bring the soup to a simmer; cook for 15-20 minutes or until potatoes are tender.
Return the browned beef to the pot.
Stir in the shredded cheddar cheese until fully melted and combined.
Serve hot, garnished with diced dill pickles.