Remove prime rib from refrigerator 2 to 3 hours before cooking to bring to room temperature.

Preheat oven to 450°F. Mix softened butter, minced garlic, kosher salt, thyme, rosemary, and black pepper in a bowl.

Pat dry the prime rib with paper towels and coat fully with the herb butter mixture.

Place bone-side down in a roasting pan. Add quartered onions if making au jus.

Roast at 450°F for 20 minutes to sear and create a golden crust.

Reduce oven temperature to 325°F and continue cooking until internal temperature reaches 120°F for medium-rare (use meat thermometer for accuracy).

Remove from oven and tent loosely with aluminum foil. Rest for 20 to 30 minutes.

Slice off bones if tied on, then cut into 1/2-inch thick slices and serve.

For Red Wine Au Jus (optional): After removing excess fat, add up to 1/4 cup pan drippings, beef broth, red wine, and leftover herbs to the roasting pan. Simmer for about 15 minutes to reduce by half. Add cornstarch slurry if you want to thicken. Strain and serve alongside prime rib.