Preheat your oven to 400°F (200°C).
Take the top sirloin steak out of the refrigerator and let it sit at room temperature for about 30 minutes before cooking.
Drizzle 1 tablespoon of olive oil over both sides of the steak. Then, season generously with 2 teaspoons of salt and 1 teaspoon of pepper.
Heat a cast iron skillet over medium-high heat until very hot. Add the seasoned steak to the skillet and sear for about 3-4 minutes on each side.
Add 1 tablespoon of butter, 2 teaspoons of minced garlic, and 3 sprigs of fresh rosemary to the skillet.
Carefully transfer the skillet to your preheated oven and cook for about 5-10 minutes.
Once the steak reaches your desired temperature, remove it from the oven and let it rest on a cutting board for at least 5 minutes.
Slice the steak against the grain into thin strips and serve.
