How to Make It
Place potatoes in a large pot, and add cold tap water to cover. Bring to a boil over medium-high, and cook, undisturbed, until potatoes are tender, about 20 minutes.
Drain and return hot potatoes to pot. Immediately add butter, cream cheese, stock, and 1⁄3 cup of the milk. Use a potato masher to blend ingredients together. Add salt and pepper. Stir in remaining milk as necessary to reach desired consistency. Preheat oven to 250°F. Transfer mashed potatoes to a 4-quart baking dish; cover with aluminum foil, and keep warm in preheated oven until ready to serve. (Potatoes can be made up to 2 days ahead and reheated, covered, just before serving. Stir in more butter and milk if potatoes seem dry after reheating.)
Place sour cream, chives, cheese, bacon, and butter in small bowls; serve alongside warm potatoes.