Seared Tuna Tostadas

I made these when we had our friends, Eric and Leah over last week for appetizers and drinks. They are perfect to serve company because a lot of it can be done ahead of time so you can relax and enjoy.

For the wasabi paste:
1/4 cup wasabi powder
1/4 cup water

For the wonton tostadas: (I just used rice crackers and omitted this part of recipe entirely)
Vegetable oil for frying
8 wonton wrappers, cut into quarters (about 2-inch squares)

For the salsa:
1 lb. (about 4) plum tomatoes, peeled, seeded, and diced (I preferred using avocado)
4 fresh shiso leaves (or 1 Tbs. fresh cilantro), chopped
2 scallions, chopped
2 cloves garlic, minced
2 tsp. rice-wine vinegar
Salt and freshly ground black pepper to taste

For the tuna:
1 Tbs. soy sauce
1 Tbs. toasted sesame oil
1 tsp. slivered fresh ginger
Freshly ground black pepper to taste
1 lb. very fresh tuna steaks (ahi is best), cut into rectangular logs about 1-3/4 inches thick and 5 inches long
1 Tbs. vegetable oil

For the garnish:
1/2 cup crème fraîche or sour cream
1/3 cup chopped scallions

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To make the wasabi paste

At least two days before serving, mix the wasabi powder with the water to form a soft paste. Cover and refrigerate.

To make the wonton tostadas

In a deep skillet, add oil to a depth of 1/2 inch. Heat the oil to 380°F -- a rice noodle will puff into a curlicue within 3 seconds or a cube of bread will turn golden in 15 seconds. (If the oil isn't hot enough, the tostados absorb too much oil and get soggy and greasy after just a few hours.) Fry a few of the wonton squares at a time until they're crisp and evenly golden on both sides, turning them during cooking if necessary, about 5 to 10 seconds. Lift out with tongs and drain on paper towels.

To make the salsa

In a bowl, stir together the tomatoes, shiso or cilantro, scallions, garlic, and rice-wine vinegar. Season with salt and pepper.

To make the tuna

In a bowl, combine the soy sauce, sesame oil, ginger, and pepper. Marinate the tuna in this sauce for 15 min. or up to 2 hours, turning it halfway through. Heat a cast-iron skillet over high heat with 1 Tbs. oil. When the oil is very hot -- it will be smoking -- put the tuna logs in the pan and sear, 20 to 30 seconds on each side; they should be seared outside and rare inside. Slice the logs into 1/4-inch pieces.

To assemble

Put a piece of tuna on a wonton. Spread a touch of wasabi paste on the tuna (not too much; it's very hot). Top with a spoonful of salsa. Garnish with a bit of crème fraîche and scallions.