Step 1: Prepare the Steak Medallions

1. Use a sharp knife to cut the beef tenderloin into evenly sized medallions, approximately 2 inches thick. Pat the medallions dry with paper towels to ensure a good sear.
2. Rub each medallion with olive oil and season generously with salt and freshly ground black pepper on both sides.

Step 2: Make the Garlic Herb Butter

1. In a small bowl, combine the softened butter, minced garlic, parsley, thyme, and lemon zest. Mix until well incorporated.
2. Transfer the butter mixture onto a piece of plastic wrap or parchment paper. Roll into a log and refrigerate until firm.

Step 3: Sear the Medallions

1. Heat a large cast-iron skillet or heavy-bottomed pan over medium-high heat. When the skillet is hot, add a small drizzle of olive oil.
2. Place the steak medallions in the skillet, leaving space between each piece. Sear for 3-4 minutes on the first side without moving, until a deep golden crust forms.
3. Flip the medallions and sear for another 3-4 minutes for medium-rare (internal temperature of 130°F). Adjust the cooking time based on your preferred doneness.

Step 4: Finish with Garlic Herb Butter

1. Reduce the heat to medium-low. Add a slice of garlic herb butter to each medallion. Let the butter melt and baste the steak with a spoon, spooning the melted butter over the top for added flavor.
2. Remove the medallions from the skillet and transfer them to a plate. Tent loosely with foil and let rest for 5 minutes.

Step 5: Serve and Garnish

1. Plate the medallions and drizzle any remaining butter from the skillet over the top. Garnish with fresh rosemary sprigs, cracked black pepper, and flaky sea salt if desired. Serve immediately.