Cut away the fat from around the edge of the steak while you heat a griddle or pan.
Brush the steak with oil to prevent it sticking to the griddle or pan, and then cook for 3 minutes a side plus 1 minute each side turned again (this gives you pretty griddle marks) for desirably rare meat; the lemon in the post-hoc marinade 'cooks' it a little more.
While the steak is cooking, place the thyme leaves, garlic, oil, lemon zest, juice, salt and pepper in a wide shallow dish.
Once the steak is cooked, place it in the dish of marinade for 4 minutes a side, before removing it to a board and slicing thinly on the diagonal.
Recipe courtesy of Nigella Lawson(Copyright 2007, Nigella Express, Hyperion, All Rights Reserved)