Prep the steak and potatoes. Pat the steak dry with paper towels and cut into 1-inch cubes. Season with 1/2 teaspoon salt, 1/2 teaspoon pepper, and the smoked paprika. Toss and let sit while you prep the potatoes. Quarter the baby potatoes into even pieces so they cook at the same rate.

Par-cook the potatoes (fast skillet method). In a large skillet (cast iron is best), heat 2 tablespoons olive oil over medium-high. Add potatoes, 1/2 teaspoon salt, and the onion powder. Cook, stirring every couple minutes, until fork-tender and golden in spots, about 10–12 minutes. If they brown too fast, lower the heat. Transfer to a plate.

Sear the steak in batches. Add the remaining 1 tablespoon olive oil to the hot skillet. Increase heat to high. Spread half the steak cubes in a single layer and don’t move them for 1–2 minutes to get a crust. Flip and cook another 1–2 minutes until browned outside and medium-rare inside. Transfer to a bowl and repeat with remaining steak.

Make the garlic butter. Lower heat to medium. Add butter to the empty skillet. When melted and foamy, stir in garlic, thyme, and red pepper flakes. Cook 30–45 seconds until fragrant. Don’t let the garlic brown.

Bring it all together. Return potatoes to the skillet and toss in the garlic butter to coat. Add the steak and any juices from the bowl. Toss gently for 30–60 seconds to warm through. Taste and season with more salt and pepper if needed.

Finish and serve. Sprinkle with parsley. Squeeze a little lemon over the top to brighten the richness. Serve hot straight from the skillet.