Cut buns in half and spread a 1/2 tablespoon of mustard on each side (adding more/less as desired).
Evenly divide the ham and cheese among 4 of the buns, reserving 4 slices of cheese for the end.
Add jalapeños to the tops of the ham/cheese buns, then top each with the final slice of remaining cheese. Top each sandwich with their reserved bun caps.
Wrap each sandwich in foil, place them on a baking sheet, and bake for 17-20 minutes, or until cheese has melted and the sandwich is heated through. Serve at once.
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