Occasionally I can get tuna that has been caught in Irish waters, and when I do, this is one of my favourite ways to serve the fish.

Ingredients

Failing the tuna, fat mackerel fillets are also excellent. It is crucial when sealing or searing the fish to just barely do that and not to overcook it – all you want is a thin line of external colour.

Serves 4

  • 50g radishes, very thinly sliced 
  • 4 spring onions, very thinly sliced at an angle 
  • 200g fresh tuna fillet or 4 large mackerel fillets 
  • 1 tablespoon sesame oil 
  • sea salt and freshly ground black pepper
  • 4 tablespoons micro greens or very tiny salad leaves, fresh coriander leaves and flowers, chopped fresh chives and chive flowers
     

Dressing 

  • 70g very finely chopped onion 
  • 2 tablespoons soy sauce 
  • 2 tablespoons rice vinegar 
  • 1 dessertspoon water 
  • 1 tablespoon grapeseed oil 
  • 1 tablespoon sesame oil 
  • 1 teaspoon caster sugar 
  • ¼ teaspoon dry mustard powder 
  • sea salt and freshly ground black pepper

Method

  1. First, soak the sliced radishes and spring onions in a bowl of ice water for 30 minutes to crisp up. 
  2. To prepare the tuna, heat a dry, heavy-bottomed, non-stick frying pan or a cast iron grill until very hot.
  3. Rub the tuna fillet all over with the tablespoon of sesame oil and season with sea salt and black pepper. Sear the tuna very quickly on all sides to achieve a blanched or very pale golden line of colour on the outside of the fish. The tuna should spend no more than 2 minutes in the pan. Remove the tuna from the pan immediately, allow to cool slightly and chill.
  4. If using mackerel, paint the flesh side of the fillet with the sesame oil and sear for a matter of seconds on a hot non-stick pan. Remove and chill. 
  5. Combine all the dressing ingredients, mixing well to blend the oils, vinegar and soy sauce. Taste and correct the seasoning. Keep chilled until ready to use. 
  6. To serve, spread 1 tablespoon of the dressing on each of four plates. With a very sharp knife, cut the seared tuna very thinly into slices about 3mm thick and divide between the plates in a single layer. If using mackerel, cut it into slices 3mm thick straight down through the flesh and skin.
  7. Season the fish with a little more sea salt and freshly ground black pepper and drizzle a little of the remaining dressing over the fish.
  8. Garnish the plates with the drained and dried radishes and spring onions, micro greens, herbs and flowers and serve immediately.

Tuna Sashimi with Crisped Radishes and Spring Onion