Preheat your oven to 400°F (200°C).

In a bowl, combine the crushed walnuts, chopped rosemary, salt, and pepper.

Rub the beef medallions with olive oil and season with salt and pepper.

Press the walnut and rosemary mixture onto both sides of each medallion to create a crust.

Heat a large oven-safe skillet over medium-high heat. Add a drizzle of olive oil and sear the beef medallions for about 2-3 minutes on each side until golden brown.

Transfer the skillet to the preheated oven and roast for an additional 5-7 minutes for medium-rare, or longer depending on your desired doneness. Remove from the oven and cover loosely with foil while you prepare the gravy.

In the same skillet, reduce the heat to medium and add the butter. Once melted, add the sliced onions and cook, stirring occasionally, for about 15-20 minutes or until they become caramelized and golden brown.

Stir in the beef broth, Worcestershire sauce, balsamic vinegar, and garlic powder. Bring the mixture to a simmer and cook for an additional 5 minutes until slightly thickened.

Serve the beef medallions drizzled with the velvety caramelized onion gravy and garnish with fresh rosemary sprigs. Enjoy!