Roll out a sheet of puff pastry into a rectangle. Spread with a thin layer of mustard. Top with ham and cheese.
Roll up tightly and cover with plastic wrap. Chill for 20 minutes.
Slice into 1/2" thick slices and place on baking sheet.
Bake at 375 degrees for 18 minutes.
Sprinkle with chopped, fresh parsley for color, if desired, and serve warm or at room temperature.