Lay 8 slices of bread on a clean work surface. Spread about 1/2 tablespoon of softened butter evenly on one side of each slice (this will be the exterior that contacts the skillet). If you prefer not to butter the bread, reserve 1 tablespoon butter for the skillet and leave the bread unbuttered.

Prepare interior spread

On the unbuttered side of 4 bread slices, spread 1/2 teaspoon Dijon mustard and 1/2 teaspoon mayonnaise (if using) on each. Sprinkle a pinch (about 1/8 tsp) of black pepper over the mustard on each slice.

Layer ham and cheese

Place 2 slices of ham on top of the mustard-coated side of each of the 4 bread slices. Add 2 slices of cheddar cheese on top of the ham. If using tomato or pickles, add 2 tomato slices or about 1/2 tablespoon chopped pickles per sandwich on top of the cheese.

Close sandwiches

Top each assembled half with the remaining 4 bread slices, buttered side facing out. Press gently to compact the sandwich.

Cook

Heat skillet or griddle

Place a large skillet, cast-iron pan, or griddle over medium-low to medium heat. Allow it to warm for 2–3 minutes so it heats evenly but is not smoking.

Cook sandwiches

Place 2 sandwiches in the skillet (don’t crowd the pan). Cook for 3–4 minutes on the first side, pressing gently with a spatula or a heavy pan to encourage even browning and cheese melting. When the bottom is golden brown, carefully flip and cook the other side for another 3–4 minutes until golden and the cheese is fully melted. If the bread browns too quickly before the cheese melts, lower the heat and cover the skillet loosely with a lid for 1–2 minutes to trap heat and help the cheese melt without burning the bread.

Finish

Remove sandwiches to a cutting board and let rest for 1 minute. Cut each sandwich in half diagonally, if desired.

Serve

Serve warm with your choice of sides such as pickles, potato chips, a simple salad, or tomato soup.