Make the soy-mustard sauce

1. Mix the mustard powder and hot water together in a cup to form a paste. Let sit for a few minutes to allow the flavor and heat to develop. Add the vinegar and soy sauce, mix together, and pass through a fine-mesh sieve into a bowl. Cover and refrigerate for at least 1 hour to allow the flavors to develop.

Make the beurre blanc

1. Combine the vinegar, lemon juice, vermouth and shallot in a heavy stainless steel saucepan. Cook rapidly over high heat until the liquid has almost all evaporated, about 1 to 2 minutes.

2. Add the cream and cook over medium heat until the mixture has reduced and thickened slightly, 1 to 2 minutes. Remove the pan from the heat and set aside until you are ready to serve the sauce.

3. Just before serving, place the sauce in the top of a double boiler over hot, not boiling water. Add the butter and salt and white pepper, whisk just until butter has melted. Serve immediately.

Make the ahi

1. Mix all of the blackening spice ingredients together on a plate. Dredge the ahi in the spice mixture on all sides.

2. Heat the olive oil in a nonstick skillet over high heat and sear the ahi for 15 to 30 seconds on each side for rare, 1 minute on each side for medium-rare, or to the desired doneness. Remove the ahi and cut into 20 thin slices.

3. For each serving, arrange 5 slices of ahi in a fan, pinwheel, or cross shape on the plate. Spoon or drizzle a little of the Soy-Mustard Sauce around the tuna, and then spoon or drizzle the Beurre Blanc around.

4. To garnish, arrange a small mound of the pickled ginger next to the fish and top with the daikon sprouts. Sprinkle the sesame seeds over the Soy-Mustard Sauce.