To prepare your beef and sauce:
Put a griddle pan on a high heat and let it get screaming hot. Pick the rosemary leaves off the woody stalks and finely chop. Mix with a good pinch of salt and pepper and scatter over your clean board. Drizzle olive oil over both sides of the steaks and roll them in the rosemary and seasoning.
Put the yoghurt and horseradish into a small bowl with a pinch of salt and pepper. Halve your lemon and add a squeeze of juice to the bowl. Add a splash of extra virgin olive oil and mix well. Taste and add a little more horseradish if you think it needs to taste more fiery.
To cook your beef:
Lay the steaks in your hot pan and press them down gently. Wait a minute, then turn them over. Cut the tip off the garlic clove and discard. Rub the hot, charred side of the meat with the garlic. Flip the steaks again after another minute, repeat the garlic rub, and press down again. For medium-rare meat, cook for around 3 to 4 minutes on each side. For well-done meat, cook for a few minutes more. Remove the steaks from the griddle to a plate to rest for a few minutes. Drizzle with a little olive oil to keep them from drying out.
To serve your beef:
8. Place your steaks on clean plates and spoon a good dollop of the horseradish sauce on top or next to them. Drizzle some of the lovely resting juices on top. Alternatively you can slice the steaks in half at an angle and serve them on a bed of something light and fresh, like a watercress salad, with the horseradish sauce.