french onion green bean casserole

Ingredients

• Servings: 10
• for the onions:
• 2 tablespoons butter
• 2 large yellow onions, thinly sliced lengthwise
• salt and ground black pepper to taste
• 1 tablespoon vinegar
• for the white sauce:
• 2 tablespoons butter
• 2 1/2 tablespoons all-purpose flour
• 2 1/2 cups milk
• 1 pinch ground nutmeg
• cayenne pepper to taste (optional)
• 1/4 teaspoon ground thyme
• for the topping:
• 2 tablespoons melted butter
• 2/3 cup panko bread crumbs
• 2 pounds fresh green beans, trimmed
• 4 ounces shredded gruyere cheese, divided
• 1/3 cup grated parmesan cheese

Recipe

Preparation Time: 45 mins Cook Time: 45 mins Ready Time: 1 hr 30 mins


• preheat oven to 375 degrees f (190 degrees c). grease a 9x13 inch casserole dish.
• heat 2 tablespoons of butter in a large skillet over medium heat. stir the onions into the pan; cook and stir until very soft and golden brown, about 15 minutes. stir in vinegar. transfer to a small bowl, and reserve.
• in the same skillet, melt 2 more tablespoons butter. whisk in 2 tablespoons flour. stirring constantly, cook over medium heat until the flour smells like baked pie crust, about 3 minutes. slowly whisk in milk, about 1/2 cup at a time, then whisk in nutmeg, cayenne pepper, and thyme. bring to simmer, and cook until thickened, whisking constantly, 3 more minutes. transfer to a bowl and reserve.
• melt remaining 2 tablespoons butter in clean skillet; stir in panko until all crumbs are coated; reserve.
• bring a large saucepan of salted water to a boil over medium heat, and boil beans until bright green and crisp but not raw tasting, 3 to 4 minutes. drain very well.
• spoon half of the caramelized onions into the prepared casserole dish; top with green beans. season with salt and black pepper. spread reserved white sauce over the green beans; sprinkle with half of the gruyere cheese. top with the rest of the onions, and use the back of a spoon to push onions down into sauce and cheese. top with the buttered panko crumbs, the remaining gruyere, and parmesan cheese.
• bake in the preheated oven until hot throughout and lightly browned, about 30 minutes. let sit 10 minutes before serving.