Preheat oven to 400 degrees.
Slice your King Hawaiian rolls in half lengthwise and place the bottoms in a glass baking dish.
Add your corned beef brisket on top of the rolls.
Layer sauerkraut on top of the meat.
Place slices of swiss cheese on top of the sauerkraut.
Mix all the ingredients for the mustard sauce and spread over the top of the rolls and place on top of the cheese to complete the sandwich.
Bake in the oven for about 10 minutes or until the cheese has melted and the sandwich is heated through.