In large saucepan over medium heat cook bacon until crispy, 8-10 minutes. Use slotted spoon to move bacon to paper towel-lined plate and refrigerate until soup is ready to serve. Remove all but 2 tablespoons of bacon fat from pot.
Add onions to pot and cook until lightly browned and softened, 7-9 minutes. Mix in garlic and thyme and cook until fragrant, about 1 minute. Pour in broth, and scrape up any browned bits from bottom of pot. Bring mixture to boil over high heat.
Add potatoes and 1 ½ teaspoons salt to slow cooker. Pour hot broth mixture over potatoes, and stir to combine. Cover and cook until potatoes are tender, 5-6 hours on high, or 6-7 hours on low.
Using an immersion blender, puree soup until smooth, about 2 minutes. Add cheddar and whisk it into soup until melted. Whisk in cream, green onion, and 1 teaspoon pepper. Season with salt to taste.
Reheat bacon in microwave until hot and crispy, about 30-60 seconds. Garnish soup with bacon, sour cream, and cheddar cheese. Serve.