I grew up eating bad French Dip sandwiches. Lots of them.
There were versions loaded with overcooked roast beef that viewed the ramekin of au jus as its Phone-a-Friend lifeline. Iterations that would have been perfectly fine if not for the fact that they happened to be housed inside stale bread. The list of French Dip–related offenses goes on and on.
But when the French Dip is good it is so good: Perfect, not-too-crusty bread loaded up with thin slices of rich roast beef, melty Swiss cheese, and tender caramelized onions.
So, I started making the sandwich at home. Along the way, I jotted down a bit of Sandwich Theory.
THEORY: NAIL THE GOLDILOCKS BREAD
Here's the problem with most French Dip sandwiches: The bread completely misses the mark. Sure, fluffy French rolls look great on Instagram and seem like a good idea up until the very moment you bite into them, but that pillowy softness can lead to major problems as soon the dip portion of the equation comes into play. Soft bread equals a soggy mess like this sad situation.
So, aim for a bread that falls somewhere between soft mess and overly-crusty. A good-quality baguette will do the job. Depending on freshness it may need to be lightly toasted.
THEORY: DON'T FEEL GUILTY ABOUT BUYING THE ROAST BEEF
I've spent an hour making this "quick" version of roast beef that's aided by the physics magic of the pressure cooker, and it yields near-perfect results. But, I also realize that sometimes there's just no time for that sort of thing. So, I'm giving you permission: It's totally okay to buy store-bought roast beef for a French Dip sandwich. If possible, opt for some of the housemade stuff at your local butcher or specialty foods store.
THEORY: SPIKE YOUR MAYO WITH HORSERADISH
As I've repeatedly preached, mayo is the key to all great sandwiches. The same rule applies to the French Dip sandwich. Mayo plays a crucial role in adding richness and creamy texture, while ensuring that no bite is too dry.
When it comes to the French Dip, I like to spike my mayo with fresh horseradish for a bit of low-grade heat. If you're making two sandwiches, simply grate about 2 tablespoons fresh horseradish with a microplane and fold it into 1/3 cup mayo until incorporated.
THEORY: YOU MUST USE SWISS CHEESE (AND IT MUST BE MELTED)
Cold oatmeal. Lumpy mashed potatoes. Soggy fried chicken. What do all of these things have in common? None of them are worse than biting into a toasty French Dip sandwich only to find a slice of cold, unmelted cheese. To solve this problem and make sure it never ever happens again, pop the assembled sandwich into a toaster oven or low-temperature oven for a few minutes until everything's nice and melted and the edge of the Swiss cheese curls itself onto the roast beef.
THEORY: DON'T SKIP THE CARAMELIZED ONIONS
Yes, cooking onions until they're delicate and slightly sweet can take 30-45 minutes (don't skip out at 10—they're not done yet). But your patience is one of the keys to really nailing this sandwich—the onions' silky richness is the final piece of the sandwich puzzle. Don't know how to caramelize onions? Here's everything you need to know.
THEORY: ALWAYS INCLUDE THE AU JUS
Food sidekicks can be critical. Tuna sandwiches have dill pickle spears, french fries depend on ketchup (or mayo, if you like that sort of thing), and crudité has creamy ranch dressing. Well, the French Dip has au jus, a sauce made from the roast beef's natural cooking juices. Au jus turns the sandwich into an interactive experience, allowing you to control how many bites are infused with the broth's rich, concentrated flavor.
If you took my advice and bought roast beef, never fear, you can still make great au jus. Make a big batch and use the rest for Faux Pho, a super-charged French onion soup, or just sip it out of a mug.
