Get your steak out of the fridge at least 30 minutes before cooking to bring it up to room temperature. Crumble the beef stock cube directly onto the steak, add the olive oil, and use your fingers to work it into a thick paste, coating both sides completely.
Get your frying pan over a very high heat. Do not add oil to the pan—the oil in your rub is all you need. Lay the steak into the dry, smoking hot pan.
Marco isn’t a time-and-temperature kind of chef when it comes to a quick steak. Instead of watching the clock, look closely at the raw top surface of the meat. After a minute or two, you will see tiny specks of red fluid (myoglobin) start to pop through to the surface. The moment those red beads appear, it’s your cue that the heat has traveled through and the steak is perfectly medium-rare. Flip and sear the other side to lock in the crust.
Unlike almost every other chef who tells you to rest meat on a warm board, Marco’s trick is to turn off the flame and leave the steak to rest right in the pan.
While the steak is resting in the pan, spread a thin layer of Dijon mustard over the top surface. Press your meat mustard-side down into the finely chopped parsley and spring onion tops. The residual heat will warm the herbs and soften the sharp bite of the mustard, creating an instant, fresh board sauce as you slice.