Remove the brisket roast from the refrigerator at least 30 minutes to bring it to room temperature. Preheat your oven to 450ºF (230ºC).
In a food processor, , garlic, olive oil ,apple juice, rosemary, 1/2 onion, salt, and pepper. Rub all of the compound butter on the outside of the beef and place in a roasting pan or cast iron skillet, surrounded with onion quarters.
3. Roast for 15 minutes and lower the temperature to 325ºF (160ºC). Roast until it reaches an internal temperature of 135ºF(60ºC) for medium-rare meat, approx. 45 minutes to 1 hour or more, it depends on the size of your roast.