Add butter to a large pot and turn on the sauté button. Once butter is melted, add in the onions and cook for 3-4 minutes until soft. Add in the garlic and cook for one additional minute until fragrant.
Add the chicken broth, potatoes, salt, and pepper to the pot, and stir well. Bring to a slow simmer, cover, and simmer until potatoes are soft. About 15 minutes.
Meanwhile, stir together the milk and flour in a small bowl to create a slurry. Set aside.
Once the potatoes are fully soft and falling apart, open the lid and stir in the slurry. Continue to simmer the soup for 4-5 minutes, until thickened. Stir in the 2 cups of cheddar cheese and stir until melted.
If desired, serve garnished with chopped bacon, green onions, and more cheese. Enjoy!