Spread softened butter evenly on one side of each bread slice and flip over with butter side down.
If using, spread Dijon mustard on the inside of the bread slices.
Place one slice of cheese on the bread, layer ham evenly on top, season with salt and pepper, then add the second slice of cheese.
Top with the second slice of bread, butter side facing out.
Toast in a toaster oven or sandwich press at 375°F for 5 to 7 minutes until golden and cheese is melted.
Alternatively, cook in a skillet over medium heat for 3 to 4 minutes per side, pressing gently until golden brown and melted.
Let the sandwich rest for 1 minute, then slice in half and serve warm.