Heat a large skillet or griddle over medium heat.
Stir mayonnaise and mustard together in a small bowl to make a quick spread.
Butter one side of each bread slice lightly; keep the buttered sides for the outside.
Spread the mayo-mustard on the unbuttered sides. Layer cheese and ham on half the slices.
Add lettuce, tomato, and pickles. Season with a pinch of salt and black pepper.
Top with remaining bread, buttered side out. Place sandwiches on the hot skillet.
Cook until golden and the cheese melts, about 2–3 minutes per side; press gently with a spatula.
Rest 1 minute, then slice and serve warm.