Salty and sweet come together in this warm sandwich - with ham and pear perfectly complemented by melted Gruyere cheese.
Brush one side of each bread slice with oil; spread mustard on other side. Layer half the cheese on mustard side of 4 bread slices and top with ham, arugula, pear, a sprinkle of pepper, and remaining cheese. Sandwich with remaining bread slices, mustard side down.
Heat a large skillet over medium. Working in batches if necessary, place sandwiches in skillet and weight with another skillet. Reduce heat to medium-low and cook sandwiches, pressing down firmly with skillet, until bread is golden and cheese is melted, 3 to 4 minutes per side, flipping once. Serve warm.
Fontina cheese and sliced turkey are another good combo to try in this sandwich.