1/4 cup minced shallot
1 1/2 teaspoons plus 2 tablespoons shoyu, divided
2 teaspoons toasted sesame oil, divided
1 tablespoon Dijon mustard
1 1/2 teaspoons sherry, mirin or sake
1 tablespoon natural brown sugar such as succanat or maple sugar
2 tablespoons water
1 tablespoon mirin
1 tablespoon brown rice vinegar
1 cup sesame seeds (1/2 cup white sesame seeds and 1/2 cup black for the most striking look)
2 tablespoons coconut oil or unrefined sesame oil
1. Combine the shallots, 1 1/2 teaspoons shoyu, 1 teaspoon sesame oil, Dijon, sherry and sugar in a bowl. Marinate the fish for at least 1/2 hour. The marinade has no acid, so the fish can marinate for up to 24 hours. Make sure all the pieces are coated.
2. Meanwhile, make the dipping sauce. In a small bowl, mix together 2 tablespoons shoyu, water, mirin, brown rice vinegar and 1 teaspoon sesame oil. Set aside.
3. Mix the seeds together and spread them out on a plate. Dredge the fish on both sides in the seeds.
4. Warm the oil in a medium non-stick or cast iron skillet over medium-high heat. Add the fish and sear one minute on all sides, just until the fish is seared with the center still pink. Ideally, the white sesame seeds will be golden brown ... but do not overcook the fish just to acheive golden seeds.
5. Remove the fish and place on a cutting board. If you want the fish a little more cooked on the inside, let the fish rest a few minutes before cutting. The residual heat will cook the fish a little more.
6. Fan the tuna medallions out on a plate. Serve with a small ramekin of the dipping sauce.