In saucepan, mix butter, poppy seeds, onion, Worcestershire sauce & mustard, stir until blended and melted. Pour 1/2 of mixture into bottom of baking dish.
Assemble sandwiches with ham and cheese slices. Arrange rolls in single layer in baking dish, spreading them around to soak up suace in pan. Pour rest of sauce over tops of sandwiches, cover dish and refrigeragte up to 24 hours for sauce to soak inches.
Preheat oven in 350 degrees, bake rolls for 15-20 minutes, uncovered until rolls are lghtly browned and cheese is melted.