Rub the pot roast on all sides with the sea salt, black pepper, and garlic powder.

(Note, the following step is recommended for best flavor, but is optional. If preferred, move on to the next step without searing the meat.) In a large skillet, heat 2 tablespoons of the olive oil over high heat. Sear the pot roast for 2 minutes on each side.

Place the seared pot roast in a 4- to 6-quart slow cooker.

Add the remaining 1 tablespoon olive oil over the pot roast. Arrange the onion, carrots, celery, and rosemary around the pot roast.

Pour the beef broth and balsamic vinegar around the pot roast.

Cover and cook on LOW for 7 hours or until the pot roast pulls apart with a fork.

Remove the roast from the slow cooker and slice into pieces. Serve with the onions, carrots, and celery. Garnish with additional rosemary.