Cook the Bacon: In a large Dutch oven or soup pot, cook the chopped bacon over medium heat until brown and crispy. Use a slotted spoon to remove the bacon to a paper towel-lined plate. Leave about 1 tablespoon of bacon grease in the pot and discard the rest.

Saute the Aromatics: Add the butter to the pot with the bacon grease. Once melted, add the diced onion and cook for 4 to 5 minutes until soft and translucent. Add the minced garlic and cook for 1 more minute until fragrant.

Create the Roux: Sprinkle the flour over the onions and garlic. Whisk constantly for 1 to 2 minutes to cook out the raw flour taste. The mixture will form a thick paste.

Add the Liquids and Potatoes: Slowly pour in the chicken broth and whole milk, whisking continuously to prevent any lumps from forming. Add the cubed potatoes, salt, and black pepper.

Simmer: Bring the soup to a gentle boil, then immediately reduce the heat to medium-low. Cover the pot and let it simmer for 15 to 20 minutes, or until the potatoes are completely fork-tender.

Thicken the Soup: For a creamier texture, use a potato masher to mash about half of the potatoes directly in the pot. Alternatively, you can use an immersion blender with a few quick pulses, making sure to leave plenty of potato chunks for texture.

Add the Cheese and Cream: Remove the pot from the heat. Stir in the freshly grated cheddar cheese and the sour cream until the cheese is completely melted and the soup is smooth.

Serve: Ladle the hot soup into bowls. Top each serving with the reserved crispy bacon, extra cheddar cheese, and chopped green onions.