Preheat your oven to 400°F (200°C).
Wash and dry the potatoes. Pierce each potato several times with a fork.
Place the potatoes directly on the oven rack and bake for 45 minutes to 1 hour, or until tender.
Remove the potatoes from the oven and let them cool slightly.
Cut each potato in half lengthwise and scoop out the flesh, leaving a thin shell.
In a mixing bowl, combine the potato flesh, sour cream, milk, butter, salt, and pepper. Mash until smooth.
Stir in half of the cheese, bacon, and chives.
Spoon the mixture back into the potato shells and place them on a baking sheet.
Top with the remaining cheese.
Bake for an additional 15-20 minutes, or until the cheese is melted and bubbly.
Garnish with remaining chives and serve hot.