Spread a Tbsp mustard over each puffed pastry rectangle, leaving a small border on one edge.
Layer ham and Swiss cheese on top of mustard.
Beat the egg and brush each plain border.
Keeping ingredients in tact, roll the pastry up to the egged border and seal.
Wrap each roll in plastic wrap and refrigerate for up to one day.
Preheat oven to 400°.
Cut each roll into 15 slices and place on an aluminum foil lined cookie sheet.
Bake for 20 minutes, until pastry is browned.
Arrange on platter and decorate with parsley.