French Onion Green Bean Casserole | Recipe Cart | Recipe Cart

Ingredients

• 2 tablespoons butter
• 2 large yellow onions, thinly sliced lengthwise
• salt and ground black pepper to taste
• 1 tablespoon sherry vinegar
• 2 ½ tablespoons all-purpose flour
• 2 ½ cups milk
• 1 pinch ground nutmeg
• 1 pinch cayenne pepper to taste
• ¼ teaspoon ground thyme
• 2 tablespoons melted butter
• ⅔ cup panko bread crumbs
• 2 pounds fresh green beans, trimmed
• 4 ounces shredded Gruyere cheese, divided
• ⅓ cup grated Parmesan cheese