2 tablespoons white wine vinegar
10 fluid ounces white wine
1/4 cup minced shallots
1 tablespoon wasabi paste, or to taste
1 tablespoon soy sauce
1 cup unsalted butter, cubed
salt and black pepper to taste
1 tablespoon olive oil, or as needed
1 cup chopped cilantro leaves
6 (6 ounce) fresh tuna steaks, 1 inch thick
Combine the white wine vinegar, white wine and shallots in a small saucepan over medium heat. Simmer until the liquid is reduced to about 2 tablespoons. Strain out shallot and discard, return liquid to the pan.
Stir the wasabi and soy sauce into the reduction in the pan. Over low heat, gradually whisk in butter one cube at a time allowing the mixture to emulsify. Be careful not to let the mixture boil. When all of the butter has been incorporated, stir in cilantro, and remove from heat. Pour into a small bowl, and set aside.
Heat a large skillet over medium-high heat. Brush tuna steaks with olive oil, and season with salt and pepper. Place in the hot skillet, and sear for 3 to 5 minutes on each side. Be careful not to overcook, this fish should be served still a little pink in the center. Serve with sauce.