Peel and dice 5 pounds Russet potatoes into 1-inch cubes. Add to slow cooker with 4 cups chicken broth and 1/2 cup butter.
Cover and cook on high for 4 hours until potatoes are fork-tender.
Carefully drain potatoes and return to slow cooker. Set to warm.
Add remaining 1/2 cup butter, 8 ounces cream cheese, and 1/3 cup warmed milk.
Use a potato masher to combine until smooth and creamy. Do not overmix.
Season with 1 teaspoon sea salt and 1/2 teaspoon black pepper to taste.
Garnish with fresh parsley or chives and serve immediately.