In a small skillet, toast the caraway seeds over moderate heat, shaking the pan occasionally, until fragrant, about 2 minutes; let cool. In a small bowl, mix the mustard with the honey and caraway seeds.
Spread the caraway mustard on 4 slices of bread. Top with the cheese, ham, sauerkraut and pepperoncini, then close the sandwiches.
In a large skillet, melt the butter over moderate heat. Add the sandwiches, cover and cook, turning once, until golden and the cheese is melted, about 6 minutes. Cut each sandwich in half and serve hot with the remaining caraway mustard on the side.