Luscious tuna is prepared tataki-style—seared, chilled, and thinly sliced—then served with glossy flame-roasted peppers and a bright homemade ponzu sauce. While it looks almost too pretty to eat, take one bite and you won't put your chopsticks down until it's gone!
White Ponzu Sauce, part 1: Into a jar, add bonito flakes and 3 orange slices. Lay kombu on a flat surface and use a damp towel to wipe off the crystallized white salt on both sides. Cut the kombu into smaller pieces, then score in a cross-hatch pattern. Set aside.
White Ponzu Sauce, part 2: In a small saucepan, add sake and mirin; bring to a boil over high heat. Then add unseasoned ponzu, white soy sauce, and rice vinegar. Return to a simmer; add kombu pieces and turn off heat. Stir to soften kombu; then pour contents of saucepan into the jar with oranges and bonito. Stir to combine, then set aside to cool, 1 hour. Makes about 1 cup White Ponzu Sauce. (Flavor improves after 2–3 days; store in the refrigerator for up to 2 weeks.)
Tuna Tataki, part 1: Square off the sides of the fillets for a "restaurant-quality" look. (This is optional. Save tuna scraps for another use, such as tartare or a snack over rice.) Cut each fillet in half to create four blocks of tuna. Place on a wire rack fitted into a sheet pan lined with parchment paper.
Tuna Tataki, part 2: Preheat a dry skillet over high heat. Drizzle oil over the tuna, about 1½ tablespoons per block. Season each with a pinch of salt, then rub the salt and oil into the tuna, flipping to coat evenly on all sides. Finish with a liberal sprinkling freshly ground pepper on top and bottom. When the pan is smoking hot, add 2 teaspoons of oil. Sear tuna, one piece at a time, for 3 seconds on each side. Chill seared tuna in the refrigerator. (Note: Tuna Tataki can be made a day in advance. Wrap in plastic and refrigerate overnight.)
Fire-Roasted Peppers, part 1: Turn one or two burners on a gas stove to high heat and lay the peppers directly over the flame. (Alternatively, char peppers on a grill, under a broiler, or with a kitchen torch.) Use tongs to turn peppers until they are charred on all sides. Place peppers in a bowl, cover the bowl tightly with plastic wrap, and let rest for 15 minutes. (The steam trapped in the bowl will continue cooking the peppers and loosen the skin for easy peeling.)
Fire-Roasted Peppers, part 2: Remove plastic wrap and place peppers on a work surface. Cut off the top and bottom, then slice open vertically and remove seeds. Lightly scrape your knife across the charred skin to remove; then use a damp paper towel to wipe off any remaining char and seeds. Optional: To remove additional char, dip briefly in water, then pat dry with paper towels. (Note: Peppers can be roasted 1 day ahead. Store in an airtight container in the refrigerator for up to 5 days.)
Julienne the peppers. Remove and set aside the shallot core (discard or reserve for another use); julienne the shallot. Peel, thinly slice, and julienne the garlic. Cut away ginger peel, slice, and julienne.
In a skillet over medium-high heat, add sesame oil and spread to cover the pan. Add ginger and stir to coat, then stir in garlic. Cook ginger and garlic until lightly brown and soft, 1 minute. Add shallots, stir, and sweat, 1 minute. Add slightly less than 1 tablespoon fish sauce and stir to incorporate. Let mixture cook until lightly caramelized and sticky, 1–2 minutes. Turn off heat, add peppers and stir, just to warm through and absorb the flavors. Stir in remaining fish sauce, taste, and adjust seasoning if necessary. Transfer to a plate and chill in the refrigerator, 15 minutes.
Assembly: Strain White Ponzu Sauce into another jar, pressing down on solids to extract all of the liquid. Set aside. Thinly slice scallion on a bias, then the serrano pepper, including seeds. Set aside. In an individual serving bowl, add several tablespoons peppers. Cut 5–6 thin slices (a "nigiri slice") of tuna at an angle, against the grain. (Reserve the corner piece for the chef!) Roll tuna slices like a cigar and place over the peppers in a decorative pile. Garnish with a few scallion and serrano slices. Add 2 tablespoons White Ponzu Sauce over and around the tuna. Assemble remaining plates and serve immediately.