PREP BEEF:
1. Bring Beef to room temp: Take beef out of the fridge 2 hours before cooking to bring to room temp for even cooking.
2. Preheat oven to 460°F. The beef should sit in the middle of the oven.
3. Garlic Herb Butter: Mix softened unsalted butter, minced garlic cloves, chopped fresh rosemary, chopped fresh thyme, salt, and black pepper until well combined.
4. Roasting bed: Place quartered onion, halved garlic head, thyme sprigs, and rosemary sprigs in an oven-proof skillet or roasting pan.
5. Spread a thin layer of the garlic herb butter on the underside of the beef (bone side). Place the beef on the onion and herb bed, butter-side down. Spread about 2/3 of the remaining butter on the top and sides of the beef (reserve some butter mixture for a second spread).
6. Oven Roast (initial): Roast for 20 minutes at 460°F.
7. Spread remaining butter: Remove the beef from the oven, spread the remaining butter over it. Turn the oven down to 250°F.
8. Slow Roast: Roast for about 1 1/2 hours to 2 1/2 hours, basting every 30 minutes with the juices in the pan, until the internal temperature is 122°F in the center. Check the internal temperature early.
9. Let Rest: Transfer the beef to a plate to cool off. Cover loosely with foil and rest for 20 minutes. The internal temperature will rise to 129°F (for medium rare).
GRAVY/SAUCE:
1. Place the skillet with the onion and garlic left in it on the stove over high heat. Add red wine and beef stock, simmer for 10 minutes until the liquid reduces by 2/3.
2. Lower the heat to medium. In a separate small bowl, mix cornstarch with 2 tbsp water until smooth. Add in half of the cornstarch mixture to the simmering liquid and stir. The sauce will thicken in about a minute. Add more of the mixture slowly to thicken further, if desired. This step is optional. Strain the gravy into a bowl. Pour over the beef before serving.
