Grilled Tuna with Tarragon Mayonnaise

Preparation

1. Step 1

   Whisk 1/4 cup oil, lemon juice, yolks and water in small metal bowl. Set bowl over saucepan of barely simmering water (do not allow bottom of bowl to touch water); whisk constantly until thermometer maintains 140°F for 3 minutes, about 6 minutes total. Transfer to processor. With machine running, very gradually add 1/2 cup oil in thin steady stream (if oil is added too quickly, the mayonnaise will separate and become runny). Mix in chopped tarragon. Season with salt and pepper. (Can be made 1 day ahead. Cover and refrigerate.)

   Step 2

   Prepare barbecue (medium-high heat) or preheat broiler. Drizzle additional oil over fish. Sprinkle with salt and pepper. Grill or broil about 3 minutes per side for medium. Transfer to plates. Top with mayonnaise. Garnish with tarragon sprigs.