Balsamic and Brown Sugar Short Ribs Fall Right off the Bone

Ingredients

2 tablespoons vegetable oil
8 bone-in beef short ribs (about 4 1/2 pounds)
1 teaspoon black pepper, plus more to taste
1 tablespoon kosher salt, divided, plus more to taste
1 medium-size yellow onion, finely chopped (about 1 1/4 cups)
6 garlic cloves, thinly sliced (about 3 tablespoons)
1/3 cup balsamic vinegar
1 teaspoon onion powder
1/2 teaspoon garlic powder
2 cups beef broth
1/3 cup packed light brown sugar
2 bay leaves
12 small fresh cipollini onions (about 10 ounces), trimmed and peeled
1 medium celeriac (celery root), peeled and cut into 1 1/2-inch pieces (about 2 cups)
3 carrots, peeled and cut into 1 1/2-inch pieces (about 1 1/2 cups)
Finely chopped fresh flat-leaf parsley (optional)