Whisk all of the dressing ingredients together in a small bowl, and season, to taste with salt and pepper.
Preheat a griddle pan or large frying pan over a high heat. Rub the steaks on both sides with a little oil and season with flaked sea salt. Once the pan is really hot, fry the steaks for 3 to 4 minutes on each side for medium-rare, or until cooked to your liking (don’t overcrowd the pan or you won’t get that lovely brown crust – you might need to cook them in two batches). Leave the steaks to rest on a board for a couple of minutes while you assemble the salad.
Toss the lettuce with enough of the dressing to lightly coat the leaves then divide between serving bowls. Scatter over some croutons. Cut the steaks into thick slices and arrange on top of the salad. Serve straight away.