Combine the coffee, mustard, garlic, shallot, balsamic vinegar, 1 tablespoon olive oil, brown sugar, salt, and pepper in a large dish or zip-top bag.

Remove and reserve 1/4 cup of the marinade (for use once the meat is cooked). This is optional (I sometimes forget this step).

Add the flank steak, refrigerate the meat, and marinate it for 24 hours, turning the meat every so often.

Heat the grill of your choice to medium-high.

Remove the meat from the marinade, reserving the liquid.

Pat the steak dry with paper towels, rub it all over with a little oil, and season with a little more salt.

Grill, basting with the left over coffee marinade frequently, until cooked rare to medium rare, 3 to 6 minutes per side, depending on thickness.

You don’t want to overcook flank steak, so take it off the grill when it’s slightly less done than you would like.

Let the meat rest at least 5 minutes before slicing thinly across the grain.

Combine any juices that have collected with the fresh reserved marinade (if you saved it), pouring over and around the beef and serve immediately.