1/4 cup dried small tree ear mushrooms, soaked in 1 cup cold water for 20 minutes
8 large tiger shrimp (10 ounces), shelled and cut into 1-inch pieces
1 8-ounce tuna steak, cut into 1-inch cubes
1 8-ounce skinless salmon fillet, cut into 1-inch cubes
8lb tiny bay scallops, or 8 ounces large sea scallops, cut into ¾-inch pieces
4oz ounces (about 2/3 cup) sea urchin roe (uni)
1/4 cup minced scallions
1 large avocado, halved, pitted, peeled, cut into 1-inch cubes, and sprinkled with 1 tablespoon fresh lemon juice to prevent discoloration
3 tablespoons toasted sesame seeds
A few fennel sprigs, for decoration
1/4 cup wasabi powder
3 tablespoons water
soy sauce, for serving
For the rice
Put the rice in a bowl, cover with cold water, and stir for a few seconds, then drain. The water will be cloudy. Repeat several times, until the water runs clear.
Transfer the rice to a saucepan, add the 3 ½ cups cold water, and bring to a boil, uncovered, stirring a couple of times. Cover, reduce the heat to very low, and cook for 15 minutes. Turn off the heat and let the rice rest, still covered, for
For the vinegar seasoning
Combine the ingredients in a glass bowl and heat in the microwave oven for 1 minute. Stir to make sure that the sugar and salt are dissolved.
After the rice has rested for 15 minutes, spread it out in a large gratin or other baking dish. Pour the vinegar seasoning over the top and mix it in gently. Cover until ready to serve. (The rice is served at room temperature.)
For the toppings
Mix the salmon or trout caviar with the corn oil in a small bowl, so it is loose and will be easy to sprinkle on the dish.
Drain the tree ear mushrooms and place them in a saucepan. Cover with 2 cups water and bring to a boil, then boil gently for 15 minutes; drain. (The mushroom cooking liquid can be kept for soup.)
Combine the shrimp pieces with ½ cup hot water in a skillet and cook for 45 seconds to 1 minute; the water will barely come to a boil, so the shrimp will still be somewhat translucent in the center. Drain and set aside.
For the wasabi paste
Mix the wasabi powder with the water in a small bowl, stirring to create a paste. Let sit for at least 15 minutes.
At serving time
Spread the rice on a serving platter so that it is 1 to 1 ½ inches deep. Scatter the shrimp, tuna, salmon, scallops, uni, and caviar over the top, along with the scallions, avocado, and tree ear mushrooms. Sprinkle the sesame seeds and fennel sprigs on top and serve with the wasabi and soy sauce.