Melt butter and mix in mustard, sauce and onion. Cut the entire pack of rolls in half, horizontally (keeping all top and bottom halves separately in tact). In a 9x13 inch pan, place bottom half of rolls and cover with ham and cheese. Cover ham and cheese stacks with top half of rolls. Drizzle butter mixture over top of rolls, making sure onion is evenly distributed. Refrigerate overnight. Bake uncovered at 350°F for 15-20 minutes and, once finished, separate for serving. Tips: To avoid soggy sandwiches, only use half of the butter mixture the night before and use the other half right before baking. Variations: Use Honey Ham instead of plain Ham. Use 1 1/2 tsp Onion Powder instead of Minced Dried Onion. Add 1 Tbsp of Black Poppy Seeds to Step 1.