Butter each slice of bread and sprinkle with Parmigiano, pressing to help it adhere. Invert the slices onto a work surface, cheese side down. Top four of the slices with the Swiss cheese, ham, and pickles, if using. Mix the mustard and preserves, and spread on the remaining four slices of bread. Close the sandwiches and griddle over moderate heat, turning, until golden-crisp on the outside and melted inside, about 3 minutes. Cut in half and serve right away.