Roasted Vegetable and Cod Casserole

Name: Roasted Vegetable and Cod Casserole
Ingredients: 2 3⁄4 cups thinly sliced shallots, plus 2 whole shallots; 2 tbsp. red wine vinegar; 12 cloves garlic, thinly sliced; 6 stalks celery, thinly sliced; 3 sprigs thyme; Kosher salt and freshly ground black pepper; 3 1⁄2 cups olive oil; 2 lb. celery root, peeled and cut into 1/2-inch pieces; 2 lb. parsnips, peeled and cut into 1/2-inch pieces; 4 cups heavy cream; 2 tsp. smoked sea salt; 2 large eggs; 1 lb. crustless sourdough bread, cut into 1/2-inch-thick slices; 1 lb. skinless cod fillets, cut into 1/4-inch-thick slices