Add potatoes and broth to the bowl of a slow cooker, and top with the butter cubes, onion powder, and minced garlic.
Cover and cook on high for 3-4 hours, or until the potatoes are cooked and soft.
Use a potato masher or an electric mixer to mash the potatoes to your desired consistency.
Stir in the sour cream, salt, and black pepper, taste, and adjust. Add the desired amount of warm cream and stir, until the potatoes are as creamy as you want.
Stir in any other add-ins if using.
Serve warm garnished with green onions and extra butter.