1. Pat the brisket dry with paper towels, then season all over with kosher salt and black pepper.

2. Heat the olive oil in a large skillet over medium high heat, then sear the brisket for 3 to 4 minutes per side, until deeply browned.

3. Place the sliced onion and minced garlic in the bottom of the slow cooker to form an aromatic bed for the brisket.

4. In a medium bowl, whisk together the whole berry cranberry sauce, beef broth, orange juice, balsamic vinegar, Worcestershire sauce, brown sugar, and Dijon mustard until smooth.

5. Pour the cranberry mixture over the onions and garlic in the slow cooker, then stir in the fresh cranberries, thyme, and rosemary.

6. Nestle the seared brisket into the slow cooker, fat side up, making sure it is mostly submerged in the cranberry mixture.

7. Cover and cook on Low for 8 to 10 hours, or on High for 4 to 5 hours, until the brisket is very tender and a fork slides in easily.

8. Transfer the brisket to a cutting board, tent loosely with foil, and let rest for about 15 minutes before slicing.

9. Strain off any excess fat from the cooking liquid, then pour the remaining cranberry sauce and onions into a saucepan and bring to a gentle simmer.

10. In a small bowl, stir together the cornstarch and water to make a smooth slurry, then whisk it into the simmering cranberry sauce.

11. Cook the sauce for 2 to 3 minutes, stirring often, until thickened and glossy, then remove from the heat and discard the woody herb stems.

12. Slice the brisket thinly against the grain, arrange on a serving platter, and spoon the warm cranberry glaze and berries generously over the top.

13. Garnish with extra fresh rosemary or thyme if desired, and serve hot with your favorite side dishes.