Marinate the beef: In a bowl combine 1 tablespoon light soy sauce, 1 teaspoon rice vinegar, 1 teaspoon freshly grated ginger and 1 teaspoon toasted sesame oil. Add the 140 g thinly sliced beef and toss to coat. Let rest for 8–15 minutes while you prepare the rest of the dish. WHY: A short marinade seasons the thin slices quickly and the acid (rice vinegar) slightly tenderizes the meat; sesame oil and ginger build aromatic depth without overpowering.

Par-cook the fingerlings for an even, fluffy interior: Place 150 g halved fingerling potatoes in a pot, cover with cold salted water, bring to a simmer and cook 8–10 minutes until just tender when pierced with a knife (not falling apart). Drain thoroughly and let steam-dry in the colander for 2 minutes. WHY: Par-boiling ensures the potatoes are tender inside so you can focus on crisping the exterior without overcooking the interior.

Rough the surfaces for extra crisp: Once drained, shake the potatoes in the colander or toss gently in the pot to scuff up the cut surfaces — the little ragged bits will become ultra-crispy. Season lightly with salt and pepper. WHY: Roughing the surface increases surface area and texture so the oil can make more crunchy edges.

Sear the potatoes: Heat a wide skillet (preferably cast iron) over medium-high heat until hot. Add 2 tablespoons neutral oil and swirl to coat. Add the potatoes cut-side down in a single layer (don’t overcrowd). Cook without moving for 4–6 minutes until a deep golden crust forms, then toss/turn and continue cooking another 4–6 minutes until evenly browned and cooked through. Transfer to a warm plate and keep warm. WHY: A hot pan and enough oil create Maillard browning which gives the potatoes their irresistible crunchy exterior and roasted flavor.

Cook the bok choy quickly: Wipe the skillet lightly (or use a second clean skillet) and return to medium-high. Add 1 teaspoon neutral oil. Add the thinly sliced garlic and the white parts of the scallion; stir 20–30 seconds until fragrant (don’t let the garlic burn). Add 120 g halved baby bok choy cut-side down first to get contact with the pan; cook 1–2 minutes until the cut sides begin to brown, then toss and cook another 30–60 seconds until stalks are crisp-tender. Season with a pinch of salt and a grind of black pepper. WHY: Bok choy cooks very quickly; high heat and minimal cooking preserve its bright color, crunchy stalks and fresh flavor.

Quickly sear the beef: While the bok choy rests (or in a second pan if you have one), wipe the skillet hot, add it back to high heat, and add the marinated beef in a single even layer. Sear 45–75 seconds without moving to develop color, then toss and cook another 30–45 seconds — total cook time depends on slice thickness but aim for just cooked through (medium-rare to medium). Transfer to a plate to rest 1–2 minutes. WHY: High-heat, fast searing creates caramelized edges and keeps thin slices tender; moving too much prevents color development and overcooking will dry the beef.

Make a quick pan glaze (optional but recommended): Reduce the heat to medium and add a splash (about 1 tablespoon) water or a tbsp of the reserved marinade to the hot pan to deglaze any fond (brown bits). Add the rested beef back to the pan for 15–30 seconds to pick up the glossy glaze, then remove. If using chili crisp, stir 1 teaspoon in now for both heat and savory complexity. WHY: Deglazing lifts concentrated flavors from the pan and turns them into an instant sauce that coats the beef for extra flavor.

Plate and finish: Divide the crispy fingerling potatoes between two plates, add the stir-fried bok choy, and arrange the seared beef strips on top. Scatter 1 tablespoon toasted sesame seeds and the green parts of the scallion over the beef and vegetables. Optionally sprinkle 1/2 teaspoon chili flakes or a drizzle of chili crisp for heat. Finish with a small drizzle of toasted sesame oil (a few drops) and an extra grind of black pepper. WHY: The seeds and scallion add crunch and fresh aromatics; finishing oil and pepper lift the whole dish.

Serve immediately: This dish is best eaten right away while the potatoes are crisp and the beef is warm; the bok choy keeps its pleasant snap when freshly cooked. WHY: Textural contrasts (hot-crisp potatoes, warm tender beef, crunchy greens) are central to the dish’s appeal and diminish if held too long.