Place quartered baby potatoes in a large pot and cover them with salted water. Bring the pot to a boil, then cook for 12–15 minutes until fork-tender. Drain and cool for 5 minutes. Smash each potato gently.

Pat the sirloin steak bites dry with paper towels and season generously with salt and pepper. Let rest while heating the skillet.

Heat 2 tablespoons of olive oil in a cast-iron skillet over high heat. Add steak bites in a single layer and cook undisturbed for 2–3 minutes.

Flip the steak bites and cook for 1–2 more minutes until medium-rare. Transfer to a plate and cover loosely with foil.

Add remaining olive oil to the skillet and cook smashed potatoes cut-side down for 4–5 minutes until golden. Turn and crisp the other side for another 3–4 minutes.

Reduce heat to medium-low, add butter and minced garlic to the skillet. Cook for 1 minute until fragrant, then stir in thyme.

Return steak bites to the skillet and toss with potatoes for 1–2 minutes until heated through. Adjust seasoning with salt and pepper.