In a small bowl, mix the Dijon mustard and mayonnaise until smooth. This will provide a lightly tangy binder for the sandwich and help balance the richness of the ham and Swiss.

Butter bread

Evenly spread butter on one side of each slice of bread. The buttered sides will be the exterior if you pan-fry or press the sandwich; if serving cold, you can omit the exterior butter and reserve just for toasting later.

Build

Place two slices of bread butter-side down on your work surface. Spread the Dijon-mayo mixture on the inner sides (the side facing the filling). Layer 2 slices of Swiss cheese on each bottom slice, then arrange 4 slices of ham on top of the cheese (overlap as needed). Add optional pickle slices if using, and sprinkle about 1/8 tsp of black pepper over each filling. Top with the remaining slices of Swiss, then place the top bread slices butter-side up to finish the sandwich.

Cook / Serve

Cold sandwich (ready to serve)

If you prefer a cold Ham & Swiss, slice the assembled sandwiches in half and serve immediately. The Dijon-mayo keeps the sandwich from being dry; the butter on the exterior is optional for cold serving.

Pan-seared (classic grilled)

Heat a nonstick skillet or cast-iron pan over medium heat. Place the assembled sandwich in the dry pan (buttered side down) and press lightly with a spatula. Cook 3–4 minutes until the bottom is golden brown and the cheese begins to soften. Flip the sandwich, press again, and cook another 2–3 minutes until the second side is golden and the cheese is melted. If the bread is browning too quickly before the cheese melts, lower the heat to medium-low and cover the pan for 1–2 minutes to trap heat.

Pressed / Panini-style

If you have a panini press or sandwich press, preheat it and place the assembled sandwich inside. Press and cook for 3–5 minutes (follow your press instructions) until the bread is crisp and the cheese is fully melted. If you want extra melty cheese, sprinkle the optional 1/2 cup shredded gruyère or extra Swiss on top of the ham before closing the sandwich.

Finish and serve

Remove the sandwich from the pan or press and let rest 1 minute to set. Slice diagonally and serve hot. For cold sandwiches, serve immediately. Optional: serve with a side of pickles, potato chips, or a simple green salad.