Instructions

1. Make a marinade by whisking together soy sauce, sesame oil, rice wine vinegar, vermouth, if using, brown sugar, garlic and ginger. Marinate tuna in marinade at least 5 hours and up to 8 hours, turning steaks once after 3-4 hours.
2. Combine butter, 1 teaspoon wasabi paste and cilantro; add additional wasabi to taste. Refrigerate until ready to use.
3. Prepare a gas or charcoal grill to high heat. Grill 2-3 minutes per side for rare, basting with sauce. (Check level of doneness by pushing fork prongs into the thickest part of the tuna and gently pushing flesh aside.) Divide wasabi butter over hot tuna steaks and serve.