If your baguette is not fresh you might want to warm it up to recrisp it. Toasting process: spray baguette with water and place in a 350 F oven for 5 minutes to recrisp the crust.
Slice the baguette and spread butter on both interior sides. Layer on the ham.
Add slices of cheese if using and then close the sandwich. Serve and enjoy.
Notes:
Jambon-beurre blog post: go read this jambon-beurre blog post if you want to learn more about the parts of this sandwich or read more about baguettes.
Baguettes: If you would like to make your own bread for this sandwich, I have a good baguette recipe.
Butter: if you would like to make your own butter, please go read this King Arthur Baking blog post about the best ways to make butter in your kitchen.