Brisket with Herbed Spinach Stuffing

Name: Brisket with Herbed Spinach Stuffing
Ingredients: 3 tablespoons olive oil; 2 cups chopped onions; 4 garlic cloves, finely chopped; 1 tablespoon chopped fresh thyme; 1 10-ounce package frozen chopped spinach, thawed, squeezed dry; 2 whole matzo sheets, finely crumbled (about 1 cup); 1 large egg, beaten to blend; 1 4-pound flat-cut brisket; 2 pounds onions, thinly sliced; 2 1/4 cups canned chicken broth; 3 large carrots, peeled, cut into 1-inch pieces; 3 celery stalks, sliced; 5 garlic cloves, peeled; 1 bay leaf