Add diced potatoes, diced onion, minced garlic, bacon, parsley and chicken broth to the slow cooker. Season with salt and pepper. Stir and cook for 6-8 hours on low or on high for 3-4 hours, until potatoes are fork tender.
Once the soup has cooked, add butter to a medium saucepan over medium heat and melt. Whisk in the flour until completely combined and gradually add in the heavy cream. Whisk the flour mixture until smooth. With the heat on the lowest stove setting, let the mixture cook until it starts to simmer and is getting thicker, stir occasionally.
Immediately add the cream-flour mixture to the slow cooker and stir to combine.
Using a potato masher, mash about 3/4 of the potatoes.
Stir in the shredded cheddar cheese and sour cream. Stir well, until fully combined and creamy. Taste for seasoning, add salt and pepper to taste.
Continue cooking the soup on low for 30 minutes or on high for 15 minutes.