For balsamic mayonnaise: 1 egg 2 Tablespoons balsamic vinegar 1 Tablespoon gf dijon mustard 3/4 teaspoon salt 1/8 teaspoon pepper 1 cup vegetable oil
For balsamic mayonnaise: Using a food processor blend egg, 1 tablespoon balsamic vinegar, mustard, salt and pepper. With motor running, pour oil through food tube in a slow steady stream. When oil is thoroughly incorporated mayonnaise will be light and fluffy. Transfer to a bowl and stir in remaining tablespoon of vinegar.
With a sharp knife, cut tuna crosswise, against the grain, into 1/8th to 1/4th inch slices.
Place balsamic mayonnaise into a plastic bag, squeezing it into one bottom corner. Cut off corner tip of bag to make a small opening.
Equally divide arugula among 4 plates, arranging tuna slices on top in overlapping fans. Squeeze balsamic mayonnaise over tuna slices in squiggles. Sprinkle each serving with capers and chives. Serve immediately.
It is critical to use the very best sushi grade tuna for this recipe. The tuna should also be served very cold.