Preheat oven to 400° F and arrange a rack in the center shelf.

Pierce each potato several times with a fork. Place potatoes directly on oven rack and bake until the skins are crisp and knife easily pierces the potatoes (about 50 min). Transfer to wire rack until cool enough to handle, about 10 minutes.

Set the oven to the broil setting.

Slice each potato in half lenghtwise. Using a spoon, scoop out the flesh, leaving about 1/4 inch intact; reserve the flesh for another use. Brush the insides with melted butter and season with salt and pepper. Flip potatoes over and brush skin side with butter and season with salt and pepper. Evenly space potatoes on baking sheet skin sides up and broil until the butter foams and the skins start to crisp, about 2-3 minutes (keep a close watch so skin doesn't burn). Flip the potato halves over and broil until the top edges just start to brown, about 2 to 3 minutes more.

Divide the corned beef evenly among the skins and top each with about 1 teaspoon of the dressing. Evenly divide the sauerkraut among the skins and sprinkle each with cheese.

Place in broiler and broil until the corned beef is heated through and cheese is melted and bubbling, about 4 to 5 minutes.

Serve immediately.