1/2 c. butter
1/4 c. prepared mustard
1 lg. onion, diced
2 tsp. poppy seed
Ham slices
Mozzarella cheese slices
Dozen rye or white buns

Mix first four ingredients together. Cook until thick and all melted. Butter rye or white buns with this mixture. Add 1 slice ham and 1 slice Mozzarella cheese. Wrap buns in tin foil and heat and 10 minutes or until cheese has started to melt.