Best Green Bean Casserole Recipe from Scratch

Ingredients

• 1 large onion (very thinly sliced (mandoline recommended))
• ¼ cup all-purpose flour
• ½ cup panko breadcrumbs
• ½ teaspoon salt
• ¼ teaspoon black pepper
• 2 tablespoons olive oil
• 1 tablespoon olive oil
• 1 pound mushrooms (sliced)
• 1 large onion (thinly sliced)
• 3 garlic cloves (minced)
• 2 cups 2% milk
• 3 tablespoons cornstarch
• 2 tablespoons water
• 2 teaspoons soy sauce
• ½ teaspoon black pepper
• 2 pounds frozen cut green beans
• Cooking spray