Heat oven to 375 degrees F. Separate dough into 8 biscuits. Press or roll each biscuit to form 5-inch round.
Spread each biscuit round with about 1 teaspoon mustard. Place 1 oz. corned beef, 1 tablespoon sauerkraut and 1 tablespoon cheese in center of each round. Fold in half; seal edges. Prick top with fork to allow steam to escape. Place on ungreased cookie sheet. Brush tops with egg.
Bake at 375 degrees F. for 13 to 16 minutes or until golden brown.