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Ingredients
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Tuna & Marinade
Soy-Butter Sauce
Finishing & Serving
Method
Tuna & Marinade
- 1
Prepare the tuna
Pat the tuna steak dry with paper towels. Trim any sinew and shape into an even rectangle about 1 to 1.5 inches thick so it cooks uniformly.
- 2
Make and apply marinade
In a shallow dish, whisk together 3 tbs soy sauce, 1 tbs mirin, 1 tsp lemon juice, 1 tsp grated ginger, 1 tsp minced garlic, 1 tsp sesame oil and 1 tsp black pepper. Place the tuna in the dish and spoon the marinade over so all surfaces are coated. Let sit at room temperature for 10 minutes (do not marinate longer than 20 minutes to avoid changing texture). Reserve remaining marinade.
Soy-Butter Sauce
- 3
Prepare the sauce
In a small saucepan or skillet over low heat, melt 3 tbs unsalted butter. Once melted and foaming a little, add 1.5 tbs soy sauce, 1 tsp mirin, 1/2 tsp lemon juice, 2 tbs thinly sliced scallions, 1 tsp toasted sesame seeds and a pinch (1/4 tsp) red pepper flakes. Stir gently and keep the sauce warm on the lowest heat; do not boil. Taste and adjust: add a pinch of salt only if needed (soy is already salty).
Searing & Finishing
- 4
Heat the pan
Place a heavy-bottomed skillet (cast iron or stainless steel) over high heat and let it get very hot for 3–4 minutes. Add 1 tsp neutral high-heat oil and swirl to coat.
- 5
Sear the tuna
Remove tuna from the marinade and pat lightly to remove excess liquid (reserve marinade for a moment). Place the tuna in the hot pan and sear without moving: 20–30 seconds per side for very rare (aim for a brown crust while center remains raw). If your steak is thicker (~1.5 in), sear 30–40 seconds per side. Use tongs to sear the edges for 5–10 seconds to color them. Do not overcook — the center should be translucent and cool to warm.
- 6
Finish with soy-butter
Turn the heat to low. Spoon 1–2 tablespoons of the warm soy-butter sauce over the seared tuna in the pan for the last 10 seconds to glaze the surface. Alternatively, remove the tuna to a cutting board and spoon the sauce over after resting.
- 7
Rest and slice
Transfer the tuna to a cutting board and let rest for 1 minute. Slice thinly across the grain into 1/4-inch slices for serving. Arrange slices on a platter or plates.
- 8
Serve
Drizzle additional soy-butter sauce over the tuna slices. Garnish with remaining sliced scallions, a sprinkle of toasted sesame seeds, microgreens or baby spinach if using, and lemon wedges. Serve immediately while crust is warm and center very rare.