In a small bowl, combine the butter, mustard, onion, poppy seeds and sugar. Place roll bottoms, cut side up, in an ungreased 15-in. x 10-in. x 1-in. baking pan.
Brush cut side of rolls with butter mixture.
Top each with Colby cheese, ham and mozzarella. Drizzle with half of the butter mixture.
Replace roll tops. Brush with remaining butter mixture. Bake, uncovered, at 350° for 10-15 minutes or until cheese is melted.
Notes
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