Heat the butter in a large soup pot over medium heat. Once melted, add the diced onion and cook for about 5 minutes, or until the onion becomes soft and translucent.

Sprinkle the flour over the onions and stir continuously for 1-2 minutes to form a roux. This helps thicken the soup later.

Slowly pour in the chicken broth while stirring to avoid lumps. Add the cubed potatoes and bring the mixture to a boil. Reduce the heat to low and let it simmer for about 20-25 minutes, or until the potatoes are tender.

Use a potato masher or immersion blender to mash some of the potatoes in the pot. This gives the soup a thicker, creamier texture while still leaving some potato chunks for added bite.

Lower the heat to medium-low and stir in the heavy cream, shredded cheddar cheese, and half of the bacon crumbles. Keep stirring until the cheese melts and the soup becomes creamy.

Once the soup is creamy, stir in the sour cream and season with salt and pepper to taste. Let it simmer for another 5 minutes to blend the flavors.

Ladle the soup into bowls, topping each serving with the remaining bacon crumbles, extra shredded cheddar cheese, and chopped green onions if desired.