Vegetable Casserole

Bahan-bahan (6 porsi)

• 4 tablespoons ½ stick unsalted butter
• 1 medium yellow onion (thinly sliced (about 1½ cups))
• 1 teaspoon kosher salt
• ½ teaspoon ground black pepper
• 3 g arlic cloves (minced (about 1 tablespoon))
• 1 (12-ounce) bag frozen peas and carrots mix (thawed and drained of excess water)
• 1 (12-ounce) bag frozen broccoli (thawed and drained of excess water)
• 3 tablespoons all-purpose flour
• ½ cup vegetable broth or low-sodium chicken broth
• ½ cup whole milk
• 1 ¼ cups shredded cheddar cheese (divided)
• 1 tablespoon unsalted butter
• ½ cup panko bread crumbs
• ¼ teaspoon kosher salt