In a large soup pot over medium-high heat, add one tablespoon of butter and the ground beef along with the Montreal seasoning. Cook until the beef is browned and no longer pink, then remove the meat from the pot and set it aside, keeping the fat in the pot.
In the same pot, add the remaining butter and sauté the chopped onion over medium heat until it becomes tender, which should take about 10 minutes.
Add the chopped garlic to the onions and cook for an additional 2 minutes, stirring occasionally.
Sprinkle the flour over the onion and garlic mixture, stirring well and cooking for 3 to 5 minutes.
Pour in the milk and beef stock, stirring to combine and create the soup base.
Add the shredded cheddar cheese to the pot, stirring until it melts and the mixture is smooth.
Incorporate the diced celery, cubed potatoes, and the cooked beef into the soup. Bring the mixture to a boil.
Once boiling, reduce the heat to a simmer, cover the pot, and cook until the potatoes are tender, which should take about 10 to 12 minutes.
Serve the soup hot, garnished with diced dill pickles on top.
