Pat the beef tenderloin dry with paper towels. Trim any silver skin or excess fat for a neat cylindrical shape. Generously season the surface with kosher salt and freshly ground black pepper, pressing lightly so it adheres.

Sear

Heat a heavy skillet or cast-iron pan over high heat until smoking. Add 1 tablespoon neutral oil and swirl to coat. Place the beef in the pan and sear, turning every 20–30 seconds to brown all sides evenly for about 2–3 minutes total until deeply browned on the exterior but still rare inside. Use tongs and work quickly.

Rest and chill

Transfer the seared beef to a cutting board and let rest for 5 minutes uncovered to stop carryover cooking. For clean thin slicing, place the beef in the refrigerator (or freezer for 10–12 minutes) until slightly firm but not frozen — this makes the next step easier and preserves a rare center.

Slice

Using a very sharp knife, slice the beef across the grain into paper-thin slices (about 1/8-inch or less). Fan the slices out on a chilled serving plate or individual plates, overlapping slightly.

Spicy ponzu sauce

While the beef rests, combine 4 tablespoons ponzu, 1 tablespoon soy sauce, 1 teaspoon mirin, 1 tablespoon fresh lime juice, 1 teaspoon Sriracha (adjust for heat preference), 1 teaspoon grated fresh ginger and 1 teaspoon toasted sesame oil in a small bowl. Whisk gently until smooth. Taste and adjust: add more ponzu or lime for brightness, more Sriracha for heat, or a pinch of sugar if you want a touch of sweetness.

Transfer most of the sauce to a shallow dipping bowl or drizzle bowl; reserve 1–2 teaspoons to lightly brush the sliced beef just before serving.

Garnish & assembly

Lightly brush the reserved 1–2 teaspoons of ponzu sauce onto the beef slices to add sheen and flavor. Arrange the fanned beef slices on the serving plate.

Drizzle a thin ribbon of the remaining ponzu sauce over the beef or serve the sauce alongside for dipping, depending on presentation preference.

Scatter thinly sliced scallions and toasted sesame seeds across the top, and add microgreens or cilantro and pickled ginger on the side if using. Serve immediately so the beef remains slightly warm in the center and the exterior still crisp from searing.