This is an updated recipe, from the point at which i tried it with mackerel. It gives mackerel an incredibly milder flavour, as you remove the skin after it cools down.
For mackere, get your fillets cleaned & pin boned (you can just cut out the mid section of the fillet where all the little bones are, in a thin strip and discard).
Use enough to fit snugly on the bottom of a small deep ish pot/ pan. You ll cover these in oil, so, think of how you ll be able to do that minimising oil amount / volume.
Get a fattier chunk of line caught tuna ; you can spot these from the shape. Toro or chu-toro (the bit just next to the uber pricy and hard to find O-toro, which is pure belly cut) is best, but you ll often see a 'loin' cut, which is smaller rounder and has a bit that sticks out ; This 'nose' of the cut is marbled with fatty rings, and thats the one you should get for this. You can even find a cut that has that nose left attatched on a fillet at a supermarket or your local fishmonger sometimes. It wont be as fatty but its what we need.
This is still worth doing with a lean loin steak, just dont use your freshest sashimi grade tuna for this, maybe buy a larger slice and reserve some you cant eat on the same day for this confit next day.
-pad the fish dry well, and salt and pepper it. let rest while you simmer the poaching oil
- Mirin riece wine, a splash.**
-Olive oil (enough to cover the tuna) good & sweet (not a bitter-ish new oil) but not your best
- 1 white onion or 2 banana shallots cut in 2 halves
- 1 clove garlic
-lots of fennel seeds
-1 big bay leaf
-salt and black peppercorns, a hefty pinch.
- Sea Salt - taste the oil, you want the oil very salty - its a preservative, but also the fish needs to pick up the flavour.
First put the pepper oregano, seeds and bay - and fry them a little. Then add the rest of the poaching ingredients and get them to reach a boil, in a pan small enough and deep enough for the tuna to sit snugly on one layer, and be covered in the oil. ( Try it out before you heat the oil, with the onion halves, to make sure its the right size.)
Once it just about reaches a gentle simmer, turn right down and keep on a low simmer for the flavours to infuse. leave the infused oil alone to simmer for 20 minutes checking its not boiling.
Let cool a tiny bit, for another few minutes off the fire. It should be feeling warm to your touch (dont burn yourselves please).
Taste for saltiness. It does need to taste fairly salty.
FOR THE TUNA;
Add the tuna, cut in thick chunks, like 2inch cubes, pushing it / squeezing tight and fitting it snuggly in the pot, making sure its all covered, and bring to a gentlest simmer. You ll see a buble or two once in a while but not a proper simmer - VERY LOW HEAT, turn your hob on and off if need be, letting residual heat do the cooking.
Around 7-10 minutes should suffice.
You ll see the tuna turn pinkish white and pale, staying pink in middle. after about 5 minutes of barely any cooking (remember you ll need to not even simmer this, just keeping it at around 70-80degrees celcius) take off the fire and leave at a cool place. You dont want it to stay warm for ages.
Take out some tuna and check - it should be pink, not white (dry) and not rare (red) -
strain the oil , and let both cool down - the tuna and the oil separately.
FOR THE MACKEREL VERSION;
-put in your fillets in the oil once its COLD / room temp.
Then bring to a simmer and as soon as you see a buble turn it off. Let residual heat cook the fish mildly and gently. It takes much less time and heat than the tuna.
Crumbling the flesh in the oil after its cooled down a little, makes for a fattier but more infused flavour. You can do this with swordfish too. But the swordfish will keep less in the fridge (its leaner) and if you left the skin on, once its cool do take it off. Its preferd to leave the skin on to cook, and take it off later.
** Mirin wine is an edit I made recently, substituting the white wine as the latter is too acidic and will break up the texture of your fish after a couple of days in the kilner jar.
Use at room temperature and serve on beans soy and toasted sunflower seeds, toss in linguini and parsley, on borlotti beans as in the ventresca recipe, or make a salad with it.
This, i think, is one of my favourite ways of cooking my favourite meat / fish ever.
Of course, hot seared tuna is delicious and probably the best thing to do with a good day-fresh sashimi-grade tuna. But this competes if done properly and carefully.
It melts like butter and the flavouring can vary as much as your appetite - use allspice fennel rosemary saffron, try with brandy in the poaching liquid, the variations are endless. Just make sure you stay on top of that fire, and Not let the liquid get too hot.
- From recent experimentation, i d suggest to omit anything acidic in the infusion of the oil, like lemon peel or zest, white wine unless you ve burnt off every hint of acidity in a pan first, as it spoils the texture after a day or so, and its tanginess could suit it for a salad ingredient but it can be too strong as the flavours infuse, overpowering the other more subtle ingredients, let alone the tuna.