Spread the softened butter evenly on all four sides of the bread slices. Sprinkle a touch of garlic powder on the outer sides and a touch of salt on the inner sides of the bread.
Preheat a skillet over medium-low heat (or set an electric griddle to 275°F). Place both slices of bread in the skillet and cook for 1 minute.
Flip both pieces of bread so the toasted side is up. Spread mayo on one slice and mustard on the other.
Layer the cheese slices and then the ham on top of the bread with mayo. Place the other slice of bread on top with the mustard side touching the ham.
Cook the sandwich for 3 minutes, then flip it over. Cook for an additional 2–4 minutes, or until the bread is golden and crisp and the cheese is melted. Lower the heat if the bread browns faster than the cheese melts.
Notes
Storage: Enjoy this sandwich fresh for the best flavor and texture. If you have leftovers, wrap them tightly in foil or plastic wrap and store them in the fridge for up to 1 day. Reheat on a skillet or in the oven to keep the bread crisp.