For the grilled lamb steak, rub the steak with the olive oil and season with salt and freshly ground black pepper.
Heat a griddle pan and chargrill the lamb for 4-5 minutes on each side, or until cooked to your liking. Remove from the pan and set aside to rest in a warm place.
For the creamed leeks, heat the oil in a pan and gently fry the onion until softened but not coloured.
Add the garlic and cook for one minute.
Add the leeks and white wine and simmer for 2-3 minutes.
Add the double cream and simmer for a further 2-3 minutes, until slightly thickened. Season, to taste, with salt and freshly ground black pepper.
To serve, place the creamed leeks onto a serving plate and top with the grilled lamb steak.