This recipe, adapted from "Martha Stewart Hors D'Oeuvres Handbook," is perfect for parties and casual gatherings.
In a medium skillet over medium heat, melt 1 tablespoon of butter. Add chopped pears and cook, stirring, until just tender, 1 to 2 minutes. Increase heat to medium-high. Sprinkle pears with sugar and continue cooking until golden brown and caramelized, 5 to 7 minutes more. Add vinegar and swirl pan until liquid is absorbed. Remove from heat and transfer pears to a plate; set aside.
Melt 1 tablespoon butter in the same skillet over medium heat. Add pear slices, in batches if necessary, and cook until lightly browned, about 3 to 4 minutes per side. Remove from heat and set aside.
Spread the remaining 2 tablespoons butter over one side of each slice of bread. Lay buttered-side down on work surface and spread opposite side generously with mustard. Slice bread in half diagonally. Top half of the diagonal slices with 1 slice of pear, 2 slices of ham, and 2 slices cheese; top with remaining diagonal slices.
Heat a clean medium skillet over medium heat; working in batches, cook 5 to 6 sandwiches at a time, turning once, until cheese is melted and sandwiches are golden brown, about 1 1/2 minutes per side. Cut each sandwich in half to make two dozen hors d'oeuvres, if desired. Garnish each sandwich with 1/2 to 1 teaspoon reserved chopped pear mixture; serve immediately.