Place the potatoes and chicken broth into a 6-quart (or larger) slow cooker. Sprinkle with salt, pepper, and garlic powder. Slice 1 stick of butter and place over the potatoes.

Cover and cook on low for 6 hours or high for 3 hours, until potatoes are fork-tender.

Turn off the slow cooker and carefully drain off the broth.

Add the remaining butter, cream cheese, and sour cream (if using). Cover for 10 minutes so everything melts into the hot potatoes.

Mash with a potato masher or beat with a hand mixer, slowly adding 1 cup of milk or cream until smooth and creamy. Add more as needed for your preferred consistency.

Taste and adjust seasoning. Garnish with parsley or chives before serving.