Cook bacon in a skillet over medium heat until crispy. Remove bacon and set aside, reserving about 2 tablespoons of bacon grease.
In the slow cooker, combine cubed potatoes, chicken broth, milk, butter, salt, and pepper. Stir to combine.
Cook on low for 4-6 hours or on high for 2-3 hours, until potatoes are tender.
Once potatoes are tender, mash some of the potatoes against the side of the slow cooker with a spoon to thicken the soup. Alternatively, you can remove a cup of soup, mash the potatoes, and return to the pot.
Stir in the heavy cream and shredded cheddar cheese. Cook for another 15-20 minutes, or until cheese is melted and soup is heated through.
Ladle soup into bowls. Top with reserved crispy bacon, and additional shredded cheddar cheese, and a dollop of sour cream if desired.
Notes
For a richer flavor, you can use half-and-half instead of milk. Ensure potatoes are fully tender before mashing.