Keep the tuna well chilled. Pat the tuna dry with paper towel and trim any sinew. Using a sharp knife, cut the tuna into very small, uniform 1/4-inch dice. Place diced tuna in a chilled bowl.

Combine aromatics and seasonings

Add the finely minced shallot, chopped capers, and sliced chives to the tuna. Sprinkle in the sea salt and freshly ground black pepper and gently toss to distribute.

Make dressing and toss

In a small bowl, whisk together the lemon juice, extra-virgin olive oil, black truffle oil, Dijon mustard, and soy sauce until emulsified. Pour the dressing over the tuna mixture and gently fold until evenly coated. Taste and adjust seasoning — add a touch more lemon or salt if needed. Chill the tartare for 10–15 minutes to allow flavors to meld, but do not over-chill (you want the tuna slightly cool, not cold).

Finish & Garnish

Plate tartare

Use a ring mold (2.5–3 inches) or small scoop to portion the tartare onto chilled plates or onto toasted brioche rounds. Press gently to compact, then lift the ring mold carefully to retain shape. If serving on crostini, place a small bed of microgreens on each toast and top with the tartare portion.

Add caviar and final touches

Spoon about 1 tablespoon (roughly 0.5–1 oz depending on preference) of caviar on top of each portion of tartare or place a small quenelle of caviar beside the tartare. Finish with a very light drizzle of truffle oil if desired (a few drops), a sprinkle of lemon zest, a pinch of flaky sea salt, and a few microgreens. Serve immediately with the remaining toasted brioche or crostini on the side.