Spread the mustard on the bottom of the baguettes.
Top off with cheese, arugula, salami, and prosciutto.
Place the top of the baguette overtop, slice the sandwich in half, and serve.
Notes
The key to any great sandwich is fresh bread. If you’re not making your own baguettes, I recommend buying and using your bread within 1 to 2 days. Nothing quite ruins a sandwich like stale bread that’s impossible to rip apart and chew.Toasted vs. untoasted: I didn’t bother toasting the baguettes because I love their soft bite. If you prefer crunchy toasted bread, place the halved baguettes cut-side-down on a baking sheet and lightly toast them in a 300ºF oven for about 10 minutes or until golden.Layer strategically: I always spread the Dijon (or whichever condiment I’m using) over the bread first, then I’ll add the shredded cheese. This is like a moisture barrier that prevents the greens and salty meats from making the bread soggy.Try the “v cut”: When my baguettes aren’t quite as soft as I like, I’ll cut a "v" in the top and fill the “pocket” with all my toppings. This makes the sandwich much easier to eat. More topping ideas: You can also add sliced cucumbers, avocado, pickled red onions, fig jam, soft green herbs, shredded chicken, hard-boiled eggs, or anything else you like on this sandwich.Make-Ahead: When I don’t demolish this sandwich ASAP, I’ll wrap it up in a layer of parchment paper, move it to the fridge, and eat it for lunch the next day.How to Store: Wrap up the assembled sandwiches in plastic or parchment paper and keep them in the fridge. Remember that the bread will start to dry out the longer it’s refrigerated, so try to eat the sandwiches within 1 or 2 days. They do not freeze well.