Preheat oven to 350 degrees.
Cut warm baked potatoes in half (lengthwise). Scoop out soft center of each half and drop in a medium bowl. Leave a thin wall of baked potatoes around each skin to help hold the filling.
For easy clean up, line a baking sheet with foil or parchment paper (optional). Arrange potato skins on the baking sheet. Set aside.
Use a masher or large spoon to mash together potatoes, melted butter (or margarine), sour cream, and milk. If mixture appears dry, add another 2 tablespoons of milk. Season with salt and black pepper as preferred.
Spoon or pipe mashed potato into skins. Top with shredded cheese, crumbled bacon or chopped smoked sausage. Bake at 350 degrees for 15 minutes or until warmed through and melty.
Top with chives and serve warm.