If you can’t find yuzu kosho, combine 1½ tsp. orange juice, and a pinch each of finely chopped serrano and kosher salt.
- 1 tablespoon crème fraîche or sour cream
- 2 serrano chiles, seeded, finely chopped, divided
- 2 tablespoons fresh lime juice, divided
- 4 ounces sashimi-grade skinless, boneless yellowtail fillet
- 1 teaspoon finely chopped shallot
- ½ teaspoon finely grated peeled ginger
- 1 radish, trimmed, thinly sliced
- Cilantro leaves with tender stems and thin fancy crackers or crispbread (for serving)
- Yuzu kosho can be found at Japanese markets and some specialty foods stores.
Mash avocado with garlic, crème fraîche, half of serranos, and 1 Tbsp. lime juice in a small bowl until mixture is mostly smooth; season with salt.
Hold your knife at a 45° angle and slice fish with the grain into ½" slices (use a sharp blade and aim for one long, clean stroke). Cut each slice crosswise into ½" pieces.
Combine oil, fish sauce, shallot, ginger, yuzu kosho, remaining serrano, and remaining 1 Tbsp. lime juice in a medium bowl. Add yellowtail, season with salt, and gently toss crudo to combine.
Spread avocado mixture on plates. Top with yellowtail, radish, and cilantro. Serve with crackers.