This fish dish comes from the legendary literary agent Ed Victor and is one of his favourite summer suppers to cook at home - ideally in the garden, as he's a maestro of the barbecue.

"The best place I know of to buy fresh, sushi-grade tuna is on Long Island," says Ed, a native New Yorker. "When the catch is brought ashore in the morning, some of the first customers there are Japanese. I've seen Long Island-caught tuna sold for sushi the following morning in Tokyo's markets. If the Japanese import it, it's got to be good."

Ingredients (serves 2):

2 sushi-grade tuna steaks, one-inch thick (don't worry if you can't get to Long Island, any good fishmonger will sort you out).

For the marinade:

50ml soya sauce

50ml cooking sherry

50ml extra-virgin olive oil

1 tablespoon finely chopped fresh ginger root

1 tablespoon grated orange or lemon peel

1 or 2 garlic cloves, crushed (optional)

"Combine the marinade ingredients in a shallow dish. Marinate the tuna steaks in the fridge for one to two hours, but no longer or they will turn mushy. Switch on your kitchen grill to its highest heat or, if cooking outdoors, make sure your barbecue is fired up and hot well in advance. Remove the tuna steaks from the marinade and place them on the grill pan or barbecue. Cook them for four minutes on each side, basting constantly with the marinade juices. When you're basting them over an open-fire barbecue, the olive oil in the marinade will flame, giving a tasty seared finish to the tuna. Serve with boiled or barbecued corn-on-the-cob brushed with lashings of melted butter - unless you're following a low-fat diet, of course. Healthy eaters could try a large, juicy beefsteak tomato as an accompaniment, sliced and topped with sea salt, extra-virgin olive oil and a single basil leaf."

The Obvious Diet, by Ed Victor, is published by Vermilion at £9.99