Grease the slow cooker insert with butter or cooking spray.
Place the potatoes in the slow cooker. Add the broth and milk and season lightly with salt and pepper.
Cook on high for 3 to 4 hours or on low for 6 to 7 hours.
Using a masher, mash the potatoes until smooth. Add the butter and stir to combine. Add the Half and Half and sour cream and mix well. Add additional Half and Half, if needed, until you reach your desired consistency.
Season with salt and pepper to taste and serve. You can keep the mashed potatoes warm in the crock pot until ready to serve.
Notes
Potatoes cooked with milk produce creamier mashed potatoes, however you can use just chicken broth to cook the potatoes if you prefer (1 cup).
For richer, creamier potatoes, use heavy cream instead of Half and Half.
For lighter potatoes you can use milk instead of Half and Half and cook the potatoes just in broth (1 cup).