Tataki of Tuna with Broccoli, Soy and Strong Japanese Mustard

• salt and pepper
• 500 g (1¼ lb) very fresh tuna, cut from a middle section in one piece

Season the tuna thoroughly and heat a ribbed grill pan as hot as possible. Prepare a container of iced water in which to immerse the tuna after cooking.

Pan fry the tuna on all sides for 1 minute each. Immediately plunge into the iced water to arrest the cooking process. Remove from the water as soon as the tuna is cold, pat dry and refrigerate.

Blanch the broccoli in boiling wa