Jamie Oliver's steak sandwich isn't your ordinary 'wich. Caramelized onions, sharp mustard, and lemony watercress means you'll want to buy extra flank steak at the butcher so you have leftovers.
*What can I use instead of flank steak?
This recipe is written specifically for flanks steak and, obviously, will be the best with that delish steak. However…if you can’t manage it, then a slab of skirt steak will also make the cut. Both are leaner cuts that need to be prepared in the same way. Finally, chuck steak is another option that will come pretty close as long as you slice it thinly, across the grain.