Remove the brisket from the fridge 30 minutes before cooking to bring it to room temperature. Rub the meat with olive oil, then sprinkle generously with a mix of salt, black pepper, dried thyme, dried rosemary, garlic powder, and onion powder, ensuring even coverage for maximum flavor.

Dice the yellow onion and shallot, then slice the garlic cloves. In a large saucepan, heat a tablespoon of olive oil over medium heat. Add the prepared onions, shallots, and minced garlic, sautéing them for 5 minutes until they become tender and fragrant.

Stir in the cranberry jelly, Worcestershire sauce, and Guinness, mixing thoroughly. Allow the sauce to simmer for 10 minutes, stirring occasionally. This cooking helps to meld the flavors together, resulting in a rich sauce perfect for drenching the brisket.

Preheat your oven to 250°F. In a high-sided roasting pan, pour half of the prepared sauce to create a flavorful base. Add the sautéed onion mixture evenly in the pan, then place the brisket fat side down. Pour the remaining sauce over the brisket, ensuring it is well coated.

Scatter the red potatoes and dried cranberries around the brisket in the pan, allowing them to absorb the delicious flavors as they cook. Garnish the dish with fresh rosemary and thyme sprigs, then cover the pan with aluminum foil to retain moisture during roasting.

Place the roasting pan in the preheated oven and cook for 4 hours. The brisket is done when it is fork-tender and easily shreds apart, filling your kitchen with irresistible holiday aromas that hint at the delightful meal to come.

Once cooked, remove the brisket from the oven and let it rest for 30 minutes, covered with foil to keep it warm. This resting period is crucial for ensuring juiciness. After resting, slice the brisket against the grain and serve it with the potatoes and sauce for a festive presentation of your Cranberry Holiday Beef Brisket.