Preheat the oven to 350 degrees F (175 degrees C) with an oven rack in the middle position. Pierce potatoes all over with a fork. Put potatoes on a baking sheet and bake until tender when pierced with a knife, 1 hour to 1 hour 15 minutes. Remove from the oven and set aside until cool enough to handle, about 10 minutes.
Slice potatoes in half lengthwise; scoop flesh into a large bowl. Return the potato shells to the baking sheet.
Add sour cream to the potato flesh and mash with a handheld potato masher until smooth. Add corned beef, sauerkraut, Swiss cheese, chives, salt, and black pepper; fold in until just combined. Spoon potato mixture into reserved potato skins (about 3/4 cup in each).
Bake in the preheated oven until cheese is melted, about 15 minutes. Increase oven temperature to broil. Broil until lightly browned in spots, about 5 minutes. Remove from oven. Drizzle with dressing and garnish with chives.
