Broccoli Wild Rice Casserole

Name: Broccoli Wild Rice Casserole
Ingredients: 2 cups uncooked wild rice; 8 cups low-sodium chicken broth or stock, plus more if needed for thinning; 3 heads broccoli, cut into small florets; 8 tablespoons (1 stick) butter; 1 pound white button or cremini mushrooms, finely chopped; 1 medium onion, finely diced; 2 carrots, peeled and finely diced; 2 stalks celery, finely diced; 1/4 cup all-purpose flour; 1/2 cup heavy cream; 1 teaspoon salt, or more to taste; 1 teaspoon black pepper, or more to taste; 1 cup panko breadcrumbs; 2 tablespoons minced fresh parsley