FOR THE SPICY CITRUS SAUCE:
2 tablespoons bonito flakes
1 large egg yolk
2 tablespoons fresh lime juice
1 tablespoon fresh orange juice
2 teaspoons sriracha hot sauce
3/4 teaspoon salt
1/2 cup plus 3 tablespoons grapeseed or other unflavored oil
For the tuna:
Vegetable oil, for deep-frying
3 large egg whites
2 tablespoon cornstarch
1 12-ounce piece sushi-grade tuna, cut into four 4-by-1 1/2-inch pieces
8 4-inch round rice crackers, ground to small crumbs
2 scallions, white part only, thinly sliced.
1. For the spicy citrus sauce: Place bonito flakes in a small bowl and cover with 3 tablespoons hot water. Allow to sit for 10 minutes, then strain through a fine-meshed sieve, squeezing out as much liquid as possible.
2. Transfer liquid to a blender. Add egg yolk, lime juice, orange juice, sriracha and salt. Pulse to mix. With blender running at medium-high speed, slowly drizzle in the oil until mixture is thickened. Transfer to a covered container and refrigerate until ready to serve.
3. For the tuna: Pour oil to a depth of three inches in a heavy, deep saucepan and heat to 400 degrees on a deep-fat thermometer. Meanwhile, combine egg whites and cornstarch in a shallow bowl, and whisk until smooth. Coat tuna pieces in mixture, then dredge in rice-cracker crumbs, making sure surface is covered.
4. Carefully transfer tuna to hot oil, turning once, until deep golden brown, about 15 seconds a side; tuna should remain rare in center. Remove carefully and drain on paper towels. Cut tuna crosswise into 1-inch pieces, and arrange decoratively on serving plates. Stir scallions into citrus sauce, and spoon onto plates. Serve immediately.
Yield: 4 servings.