Take the steak out of the fridge 15 minutes before cooking. This helps it cook evenly.
Cut the steak into even, bite-size pieces. Pat them dry with paper towels.
Heat a cast iron skillet over high heat until very hot.
Add olive oil to the pan. Carefully add the steak in a single layer. Do not crowd the pan.
Let the steak cook without moving for 2 minutes to form a crust.
Flip the pieces and cook another 1–2 minutes until browned.
Transfer the steak to a plate and lower the heat to medium.
Add butter to the skillet. Once melted, add the garlic and stir for 30 seconds.
Return the steak to the pan. Toss gently to coat with garlic butter.
Cook for 30–60 seconds, then remove from heat.
Taste and adjust salt and pepper. Sprinkle with parsley if using. Serve hot.