These Cuban-style ham and cheese sandwiches are also called cubanos.
Split ficelles and spread with mustard and mayonnaise. Layer two halves with cheese, pickle, and ham; top with remaining halves.
In a heavy skillet, heat 1/2 tablespoon butter over medium heat. Cut one sandwich on an angle into 3 or 4 pieces to fit in pan. Place in pan, cover with foil, and place a slightly smaller heavy skillet on top. Place a full teakettle or other heavy object in the skillet to weight the sandwiches. Cook until bread is brown and crisp, about 3 minutes. Turn and cook the same way until crisp on other side and cheese is melted, about 2 more minutes; wrap in foil to keep warm. Melt remaining butter; repeat process with remaining sandwich.
Let cool for a minute or two before cutting diagonally into bite-size pieces.
The sandwiches can be made several hours ahead of time and kept wrapped in plastic until you're ready to cook them.