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Cut a baguette in half lengthwise using a serrated knife. Spread butter on one side of the baguette and the mustard on the other. Layer the ham and cheese on the bottom half of the baguette. Cover the sandwich with the top half of the baguette and press down on it lightly. Cut the sandwich into 4 to 8 equal-sized portions. Serve the sandwiches immediately.
Try to get one that is about 26 inches (66.04 centimeters) long. You can choose to include the heel, or cut it off. If you don't like mustard, then simply use more butter instead. Make sure that the butter is at room temperature, however; this will make it easier to spread. If you can't find any Dijon mustard, you can use regular mustard instead. For extra flavor, use salted butter. For extra flavor and crunch, you can add some slicked cornichons as well. This will "seal" the sandwich and help keep it together. Don't press down so hard that the crust cracks, however. If the sandwiches are not holding together, you can stick a sandwich/club frill toothpick down the center of each one. If you won't be eating them right away, you can wrap them up tightly with plastic wrap, and store them in the fridge for the next day.