Tuna Tartare with Black & Blue Sauce

Makes 6-8 servings
Black & Blue Sauce Slightly adapted from Nick's Fish Market

For the tuna tartare:
1/2 pound very fresh ahi tuna, cut into a small dice
1/2 medium Hass avocado, cut into a small dice
1 scallion, minced - plus 2 scallions for garnish
2 medium limes
1 teaspoon soy sauce
2 tablespoons olive oil
1/4 teaspoon wasabi paste
Kosher salt and freshly ground black pepper
1 teaspoon toasted sesame seeds, plus extra for garnish

Black & Blue Sauce:
1/3 cup Dijon Mustard
1/4 cup soy sauce

1 English cucumber, sliced lengthwise very thin
1 package thin, plain cocktail crackers

Prepare the tuna tartare by first whisking together in a medium bowl the zest and juice of 2 limes (about 1 1/2 tablespoons), soy sauce, olive oil, wasabi paste, dash of salt and pepper and 1 teaspoon of the sesame seeds. Gently toss in the tuna, avocado and scallion, turning to coat well; cover and refrigerate for 30 minutes.

For the sauce, whisk together the Dijon mustard and soy sauce in a small bowl; cover and refrigerate.

To make the cucumber cups, slice a washed and dried English cucumber lengthwise into long, thin strips. A mandoline slicer works well, start by first making one horizontal end-to-end slice along the middle of the cucumber using a knife to remove some of the cucumber skin to facilitate easier slicing with the mandoline. Roll the cucumber slices to form small cups, pressing the ends together to seal. Stand the cucumber cups on their edges on a plate, cover and refrigerate until you are ready to assemble.

To assemble:

Fill each cucumber cup with the tuna mixture, mounding to the top. Pour a small amount, about 1 tablespoon, of the Black and Blue Sauce in the center of each serving place and carefully swirl with a butter knife to create circular pool of sauce. Place 1 filled cucumber cup on each plate in the middle of the pool of sauce. Garnish the plate and tops with 2 remaining scallions which have been sliced on the diagonal into long, thin strips. Sprinkle with additional toasted sesame seeds and serve with thin crackers.
Serve immediately.