At Ubin restaurant in Costa Rica we enjoyed tuna that had been seared with fennel seed and coriander seed. I really liked this combination and wanted to try it at home. The photo was made with my phone in bad lighting conditions.
The ingredients needed are very simple: a tuna steak, fennel seed, coriander seed, salt, and olive oil.
There is no sous vide in this recipe, but you do need a vacuum machine to get the seeds to stick to the tuna. For the best flavor and texture, you should allow some time for the salt to penetrate into the fish. Therefore the tuna should be salted and vacuum sealed with the seeds the night before or the morning before.
First season the tuna on all sides with fine table salt. The right amount of salt is a matter of personal preference, but I like to use about 1% by weight. So for a tuna steak of 300 grams (.66 lb) that would be 3 grams, or about 1/2 teaspoon of table salt.
Then put the tuna in the bag. Put the seeds on the tuna inside the bag. I used about a 1/2 tablespoon of coriander and a 1/2 tablespoon of fennel per side for a tuna steak of 300 grams (.66 lb). Spread out the seeds with your fingers. The tuna should be almost covered with seeds, but only in a single layer, and the seeds should be evenly distributed.
Then carefully turn the bag with the tuna, supporting the side with the seeds with your hand while you turn. Then put the seeds on the other side. When you are finished, carefully place the bag in the vacuum sealer, again supporting the bag with your hand.
Allow the tuna to rest in the refrigerator.
Allow the tuna to come to room temperature. Brush the tuna with olive oil on both sides before searing.
We were eating on the boat, so I used a very hot charcoal grill and direct heat, with the tuna placed very close to the heat source. Grill the tuna, turning only once, until the seeds are golden. You still want the tuna to be rare on the inside, so this only works well with a thick tuna steak. A thin steak would be overcooked before the seeds have been toasted properly.
Searing it in a very hot frying pan is easier. Because of the direct heat transfer it is easier to toast the seeds and sear the outside without overcooking the inside, also for a thinner tuna steak. Make sure to use a heavy (thick-bottomed) frying pan and preheat it well. Turn the tuna only once. (Turning more often will increase cooking the inside and decrease searing the outside, which is the opposite of what we are looking for in this case.)
Allow the tuna to rest briefly before slicing and serving.
We enjoyed a Bandol rosé with this, which is a bit more spicy than a regular Provence rosé (but a good Provence rosé would also work, or a slightly chilled Pinot Noir, especially from Germany (called Spätburgunder there)).