Prepare your ice bath first, a large bowl filled with ice and cold water. Have it ready before you touch the stove. This is non-negotiable.

Mix cracked peppercorns and flaky salt on a flat plate. Roll the beef log firmly in the mixture, pressing to adhere on all sides.

Heat a cast iron or stainless steel pan over maximum heat for 2 full minutes. Add neutral oil. It should shimmer and almost smoke immediately.

Sear the beef for 30–45 seconds per side, all four sides if it's a round log, rotating quickly. You want dark, aggressive color. Don't move it while it's searing, let the crust form.

Immediately transfer to the ice bath the moment the last side is seared. Hold it submerged for 2 minutes. This stops all carryover cooking instantly.

Remove from ice bath, pat completely dry with paper towels. Wrap tightly in plastic wrap and refrigerate for at least 15 minutes, cold beef slices far cleaner than warm.

While the beef chills, whisk together all dressing ingredients in a small bowl. Taste it, it should be punchy, savory, and bright. Adjust lemon or soy to balance.

Unwrap beef and slice as thinly as possible, 2–3mm slices ideally. A sharp knife is not optional here. Dull knives tear instead of slice and ruin the texture completely.

Fan slices on a chilled plate. Spoon dressing over the top. Add red onion, cilantro, sesame seeds, and lemon slices.

Serve immediately, or refrigerate plated and undressed for up to 2 hours before serving.