½ cup dry white wine
2 ½ Tbsp Dijon mustard
1 Tbsp coarsely chopped thyme leaves
1 Tbsp plus 1 teaspoon ground fennel
2 shallots, coarsely chopped
10 1-inch-thick tuna steaks, 8 ounce each
kosher salt and freshly ground pepper
1. In a medium bowl, whisk the olive oil with the wine, mustard, thyme, fennel and shallots. Arrange the tuna steaks on a large rimmed baking sheet and pour the marinade over them. Turn the tuna steaks to coat. Let stand for 30 minutes.
2. Light a grill or preheat a grill pan. Season the tuna steaks with salt and pepper. Grill over moderately high heat, turning once, for 4 minutes per side, until medium. Thinly slice the steaks, transfer to plates and serve.