Cook the chopped bacon over medium heat until golden and crispy, about 5 to 7 minutes. Transfer to a paper towel-lined plate, leaving 2 tablespoons of rendered fat in the pot.

Melt unsalted butter in the bacon fat over medium heat. Add chopped yellow onion and sauté for 5 minutes until soft. Stir in minced garlic and cook for another minute.

Sprinkle all-purpose flour over the onion and garlic mixture, stirring to form a roux. Cook for 1 to 2 minutes, stirring constantly until golden.

Gradually whisk in chicken broth, ensuring no lumps remain. Add diced russet potatoes, bring to a boil, then reduce heat and simmer uncovered for 15 to 20 minutes until tender.

Stir in whole milk and heavy cream. Season with kosher salt, black pepper, and paprika, simmer gently for another 10 to 15 minutes.

Using a potato masher, lightly mash some of the soup to achieve desired consistency. Mix in 1 ½ cups of shredded cheddar cheese and sour cream until melted and blended.

Ladle soup into bowls and garnish with crispy bacon, remaining cheddar cheese, sliced green onions, and fresh parsley. Serve immediately.