Bring the potatoes to a simmer: Place the baby Yukon potatoes (whole) in a pot, cover with cold water by 1 inch, add 1/2 tsp kosher salt, and bring to a gentle boil. Simmer until just tender when pierced with a knife (12–15 minutes). Starting from cold water ensures even cooking and prevents the outside from overcooking before the center becomes tender.

Drain and steam-dry the potatoes: Drain the potatoes and return to the hot pot off heat for 2 minutes so surface moisture evaporates. This prevents oil splatter and helps the potatoes crisp when smashed and pan-fried.

Smash the potatoes: On a rimmed baking sheet, press each potato gently with the bottom of a glass or a small metal spatula until it’s flattened about 1/4–1/2 inch thick. Keep them in a single layer. Smashed potatoes create more surface area for browning, resulting in a crisp exterior and creamy interior.

Pan-fry the smashed potatoes: Heat 2 tbsp vegetable oil over medium-high in a large nonstick or cast-iron skillet until shimmering. Add the smashed potatoes in a single layer (work in batches if necessary) and fry without moving for 3–4 minutes to develop a deeply golden crust. Flip and cook the other side 2–3 minutes. Transfer to a warm oven (200°F/95°C) to keep crisp while you prepare the beef. High heat gives the Maillard reaction — that caramelized crust that tastes roasted and rich.

Prep the beef and sauce while potatoes cook: Pat the steak dry with paper towels (dry meat sears better), then slice thinly against the grain into 1/8–1/4-inch strips. Season lightly with 1/2 tsp kosher salt and 1/4 tsp black pepper. In a small bowl, whisk together soy sauce, oyster sauce, honey, rice vinegar, and sesame oil. In another small cup, dissolve 1 tsp cornstarch into 2 tbsp cold water for a slurry. Cornstarch will thicken the sauce quickly without clouding it.

Heat the wok/skillet for the beef: Place a large wok or heavy skillet over high heat and let it get very hot (about 2–3 minutes). Add 1 tbsp vegetable oil and swirl. A screaming-hot pan creates instant sear and helps develop a thin crust on the meat without overcooking inside.

Flash-sear the beef in batches: Add half the beef in a single layer, don’t crowd the pan — sear 30–45 seconds without moving to get color, then toss and remove when just medium-rare (beef continues to cook later). Repeat with the remaining beef. Searing in batches prevents steaming and ensures caramelization.

Lower heat and build aromatics: Reduce heat to medium-high, add the butter and remaining 1 tbsp oil to the wok, then add the sliced onion and white parts of the scallions. Sauté 1–2 minutes until edges begin to soften and brown — this adds sweet, savory flavor. Add the minced garlic and ginger and sauté 20–30 seconds until fragrant; short cooking prevents garlic from burning and going bitter.

Add peppers and combine: Toss in the bell pepper strips and stir-fry 1–2 minutes until just tender-crisp — you want bright color and a little crunch to contrast the soft potatoes and tender beef.

Return beef and add sauce: Return the seared beef to the wok along with any accumulated juices. Pour the soy/oyster/honey mixture over the contents and bring to a simmer so flavors marry. The added juices from the beef contribute to the sauce’s depth — simmering briefly melds sweet, salty, and umami.

Thicken the sauce: Stir the cornstarch slurry (it may have settled) and pour into the wok while stirring. Cook 30–60 seconds until the sauce glazes the beef and vegetables. Cornstarch thickens rapidly and gives a glossy restaurant-style finish that clings to the ingredients.

Finish and check seasoning: Taste and adjust with a pinch of salt, a grind of black pepper, or a splash more rice vinegar if you want brightness. Fold in the green parts of the scallions and 1 tsp sesame oil for aroma, then remove from heat. Finishing with scallion greens keeps their color and fresh bite.

To serve: Spoon a bed of crispy smashed Yukon potatoes onto each plate and pile the glossy beef and peppers on top. Sprinkle with toasted sesame seeds and an extra scattering of scallion greens. Serving the beef over potatoes lets the sauce soak into the crisp tops for a perfect mouthful of savory, juicy, and crunchy textures.