Directions :

1. Place steak between two pieces of parchment paper and pound with the spiked side of a meat mallet just until tenderized—avoid thinning out the steak. Season generously with salt and pepper.
2. Place steak into a resealable bag or container. Pour in olive oil, vinegar, red pepper flakes, and oregano. Finely grate 1 garlic clove straight into the bag and mix to combine. Let marinate at room temperature for 30 minutes.
3. Remove steak from marinade and pat very dry. Peel and crush remaining 2 garlic cloves.
4. In a medium cast-iron skillet over medium-high heat, heat vegetable oil. Add steak and cook, flipping once, until a deep golden crust begins to form on both sides of the steak, about 5 minutes total.
5. Reduce heat to medium low and add butter, crushed garlic, and rosemary to pan. Using a kitchen towel, carefully grip the skillet handle and tilt pan towards you so that the melting butter forms a pool at the bottom of the skillet. Using a spoon, continually baste butter onto steak to form a deeper golden crust. Flip steak and repeat, 2 to 3 minutes in total.
6. Using a meat thermometer, check for doneness: 120-125° for medium rare, 130°F for medium. Transfer steak onto a cutting board and let rest 10 minutes.
7. Thinly slice against the grain and return to skillet to serve over the juices. Top with flaky salt.