Place the quartered potatoes in a microwave-safe bowl with 2 tablespoons of water, cover, and microwave on high 4–5 minutes, until just fork-tender at the edges but still firm in the center. (No microwave? Boil in salted water 5 minutes, then drain well.) Drain any water and pat the potatoes very dry.

Pat the steak cubes dry with paper towels. Toss with 1 tablespoon of the olive oil, the kosher salt, black pepper, smoked paprika, and garlic powder until evenly coated. Let them sit at room temperature while the skillet heats.

Heat the remaining 1 tablespoon olive oil in the large skillet over medium-high heat until shimmering. Add the potatoes in a single layer, cut-side down where possible. Cook undisturbed 3–4 minutes, then flip and cook 4–5 minutes more, until deeply golden and crisp on at least two sides. Transfer to a plate.

Return the skillet to high heat until it just starts to smoke. Add half the steak cubes in a single layer with space between them. Sear 2 minutes without moving, flip, and sear 1–2 minutes more. Transfer to the plate with the potatoes and repeat with the remaining steak. Pull them at 130–135°F for medium-rare; they carry over a few degrees as they rest.

Reduce the heat to medium-low. Add the butter to the skillet and let it melt, scraping up the browned bits. Stir in the minced garlic and red pepper flakes (if using) and cook 30–45 seconds, just until fragrant.

Return the steak bites and potatoes to the skillet and toss to coat in the garlic butter, about 1 minute. Shower with the parsley, finish with flaky sea salt if you like, and rest 3 minutes before serving so the juices settle.