Prepare your ingredients: peel and dice the russet potatoes, and dice the onion.
Place potatoes, onion, chicken broth, butter, garlic, salt, and pepper into the slow cooker.
Cook on low for 4–6 hours or on high for 3–4 hours, until potatoes are tender.
About 30–60 minutes before the soup is done, whisk heavy cream, sour cream, and xanthan gum in a bowl until smooth.
Stir the cream mixture into the slow cooker. Mix well to combine.
Cook an additional 20–30 minutes on high to thicken and develop flavors.
Taste and adjust seasoning if needed. Serve hot with garnishes like bacon, cheese, or fresh herbs.
Notes
For a vegetarian option, use vegetable broth instead of chicken broth. You can also swap heavy cream for coconut cream and sour cream for Greek yogurt. Leftovers store well in the fridge or freezer.