Step 1: Prepare the Brisket
1. Season the Brisket: Pat the brisket dry with paper towels. Season generously with salt and pepper on both sides.

Step 2: Sauté the Aromatics (Optional)
1. Sauté Onions and Garlic: In a skillet over medium heat, add a little oil and sauté the sliced onions until soft and translucent. Add the minced garlic and cook for another minute until fragrant.

Step 3: Assemble in the Slow Cooker
1. Place Brisket in Slow Cooker: Place the brisket in the slow cooker.
2. Add Onions and Garlic: Add the sautéed onions and garlic on top (if you sautéed them).
3. Mix Sauce Ingredients: In a bowl, combine the cranberry sauce, beef broth, brown sugar, soy sauce, Dijon mustard, and dried thyme. Mix well.
4. Pour Sauce Over Brisket: Pour the mixture over the brisket, ensuring it is well coated.

Step 4: Cook
1. Cover and Cook: Cover and cook on low for 8 hours, or until the brisket is tender and easily shreds with a fork.

Step 5: Serve
1. Slice and Serve: Remove the brisket from the slow cooker, let it rest for a few minutes, then slice against the grain. Spoon the cranberry sauce and onions over the top.
2. Garnish: Optionally garnish with fresh parsley.