Remove the brisket from the refrigerator 30 minutes before cooking to bring it to room temperature.

Gather your ingredients and prepare your seasoning rub by mixing salt, pepper, dried thyme, and rosemary in a bowl.

Drizzle olive oil over the brisket, coating it evenly on all sides. Apply the seasoning rub generously to enhance flavor.

Dice half of the onion and thinly slice the remaining half. Mince your shallot and garlic cloves.

In a saucepan over medium heat, heat olive oil to sauté the diced onions, shallot, and minced garlic for about 5 minutes.

Add cranberry jelly, Worcestershire sauce, and Guinness, simmering for 10 minutes to create a rich sauce.

Preheat your oven to 250°F (120°C) and pour half of the sauce mixture at the bottom of a roasting pan.

Place the sliced onions beneath the brisket and pour the remaining sauce over it. Surround with potatoes and sprinkle with dried cranberries.

Cover the pan with foil and roast for approximately 4 hours until tender and juicy.

Once done, let the brisket rest for 30 minutes to allow juices to redistribute before slicing.