Hot Ham and Cheese Sandwiches

1/4 cup butter, softened
2 tablespoons prepared horseradish mustard
2 tablespoons chopped onions
1 teaspoon poppy seeds
1 teaspoon dill seed
8 slices Swiss cheese
8 slices cooked ham
8 hamburger buns

Preheat oven to 250 degrees F.
Combine butter, mustard, onions, poppy seeds and dill seed. Spread insides of buns with this mixture. Place a slice of cheese and a slice of ham inside each bun.
Wrap buns in foil and place in preheated oven. Bake for 15 to 20 minutes, until cheese has melted.