In a small bowl, combine kosher salt, black pepper, smoked paprika, cayenne, garlic powder, onion powder, dried thyme and brown sugar. Stir to make a uniform rub.

Lightly season both sides of each tuna steak with a tiny pinch more salt if desired, then press the spice rub firmly into all sides of the steaks so they are well coated.

Searing and finishing

Heat pan

Place a heavy-bottomed skillet (preferably cast-iron) over high heat and let it get very hot for 3–4 minutes. Add the neutral oil and swirl to coat the pan; it should shimmer but not smoke heavily.

Add 1 tablespoon of butter to the pan and let it melt and foam briefly. Carefully set 2 tuna steaks into the pan, spacing them so they don’t touch.

Sear the first side for 45–60 seconds until a dark, nearly black crust forms from the spice rub. Flip and sear the second side for 30–45 seconds for rare (center cool-red). For medium-rare cook 60–90 seconds per side. Avoid overcooking — tuna is best served rare to medium-rare.

Remove the first two steaks to a cutting board and tent loosely with foil. Wipe the pan if there is heavy residue, add remaining 1 tablespoon butter and a drizzle more oil if needed, then repeat the searing for the remaining steaks.

After removing all steaks, add fresh lemon juice and chopped parsley to the pan and stir briefly to pick up any browned bits, then spoon the butter-pan juices over the seared tuna.

To serve

Slice each tuna steak crosswise into 1/3-inch thick slices against the grain to reveal the rare center.

Arrange slices over steamed rice or mixed greens. Drizzle with pan juices and serve with lime wedges and soy sauce or ponzu on the side.

Serve immediately while crust is crisp and center is tender.