I want to make french dip sandwiches for two people. What do I ask for at the butcher shop?

To be specific Boars Head London Port. Sliced paper thin. Heat up the Au Jus sauce and use tongs to dip the roast beef to warm it well before placing on the bread.

Thinly sliced roast beef is traditional, or really any kind of shaved beef. Alternatively, if you're up for a project you could make your own roast beef but you'll definitely have leftovers. It's also hard to slice it thinly enough at home.