Heat oven to 375°F. Separate dough into 4 rectangles. Onto ungreased cookie sheet, place 2 rectangles, short ends together, forming 14x5-inch rectangle. Firmly press perforations and center seam to seal.
Spread rectangle with dressing to within 1/4 inch of edges. Top with corned beef, cheese and sauerkraut. Press remaining 2 rectangles to 7x5 inches, firmly pressing perforations to seal. Spread each with 2 teaspoons mustard. Place each rectangle mustard-side down on sauerkraut, pinching center seam to seal. Brush top with water, and sprinkle with caraway seed.
Bake 18 to 22 minutes or until deep golden brown. Cut into slices. Serve warm.