1/4 teaspoon dashi powder (see Note)
1/4 cup water
2 large egg yolks
2/3 cup yellow miso
2 tablespoons sugar
1 tablespoon powdered mustard
2 teaspoons soy sauce
3 tablespoons unseasoned rice vinegar
6 (8 oz.) lobster tails
2 pounds asparagus, trimmed
1 tablespoon soy sauce
1 tablespoon fresh lemon juice
1 tablespoon fresh lime juice
1 tablespoon peanut oil
1 tablespoon toasted sesame oil
6 thick slices of toasted peasant bread, for serving
6 radishes, thinly sliced
2 scallions, thinly sliced
Black sesame seeds, for garnish
Make the Vinaigrette
In a small bowl, dissolve the dashi powder in the water. In a heatproof bowl, whisk the egg yolks with the miso, sugar, mustard, soy sauce and dashi broth. Set up an ice bath nearby. Set the bowl over a pan of barely simmering water, making sure that the bowl is not touching the water. Whisk constantly until the sauce is slightly thickened and reaches 160°, about 3 minutes. Immediately set the bowl in the ice bath to stop the cooking and whisk the sauce until cool. Whisk in the rice vinegar and refrigerate the miso vinaigrette until chilled.
Prepare the Salad
In a large pot of boiling water, cook the lobster tails until they turn bright red, about 8 minutes. Drain and let cool.
Using scissors, cut along the underside of the tails and remove the meat. Cut all of the lobster meat into 1-inch pieces, transfer to a bowl and refrigerate until chilled.
Bring a pot of salted water to a boil. Set up an ice bath nearby. Blanch the asparagus in the boiling water for I minute. Using tongs, transfer the asparagus to the ice bath to cool, then drain and blot dry. Transfer the asparagus to a small baking dish.
In a small bowl, whisk the soy sauce with the lemon juice, lime juice and peanut and sesame oils. Drizzle over the asparagus and toss gently to coat.
Add 1/4 cup of the miso vinaigrette to the lobster and toss to coat. Set the toasts on plates. Top with several spears of asparagus and a scoop of lobster and garnish with radish slices. Sprinkle with scallions and sesame seeds and serve, passing the remaining miso vinaigrette at the table.
MAKE AHEAD The vinaigrette and salad can be prepared through Step 4 and refrigerated overnight.
NOTES Dashi powder is available at many health food stores and at Asian markets.