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French Onion Green Bean Casserole – Holiday Side Dish Recipe

French onion green bean casserole combines tender green beans with a creamy sauce of deeply golden onions and mushrooms, baked under Gruyere and French-fried onions. It’s a holiday side dish with bubbling edges and a crisp, golden topping.
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Prep Time 15 minutes
Cook Time 1 hour 17 minutes
Total Time 1 hour 32 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French
Calories: 330
Ingredients Equipment Method Notes

Ingredients
  

For the casserole
  • 1 tsp nonstick cooking spray for greasing
  • 2 lb green beans frozen cut, thawed and patted dry
For the French onion sauce
  • 4 tbsp unsalted butter
  • 2 yellow onions large, thinly sliced
  • 1 tsp kosher salt
  • 1 tsp fresh thyme leaves
  • 8 oz cremini mushrooms sliced
  • 0.25 cup all-purpose flour
  • 1.5 cup low-sodium beef broth
  • 1 cup heavy cream
  • 1 tsp Worcestershire sauce
  • 0.5 tsp black pepper
For the topping
  • 1.5 cup Gruyere cheese shredded
  • 1.5 cup French-fried onions

Equipment

  • 1 9x13-inch baking dish
  • 1 12-inch skillet

Method
 

Prepare the casserole
  1. Heat the oven to 350°F.
  2. Coat a 9x13-inch baking dish with the cooking spray.
Make the French onion sauce
  1. Melt the butter in a 12-inch skillet over medium-low heat.
  2. Add the onions, salt, and thyme and cook, stirring often, for 30 to 35 minutes, until the onions are deeply golden and very soft.
  3. Stir in the mushrooms and cook for 6 to 8 minutes, until browned and their released liquid has evaporated.
  4. Stir in the flour and cook for 1 minute.
  5. Gradually stir in the broth, heavy cream, Worcestershire sauce, and black pepper until smooth.
  6. Bring the sauce to a gentle simmer and cook for 3 to 5 minutes, stirring, until thick enough to coat the back of a spoon.
Assemble and bake
  1. Add the green beans to the skillet and stir until evenly coated.
  2. Transfer the mixture to the prepared baking dish.
  3. Bake for 20 to 25 minutes, until bubbling around the edges.
  4. Sprinkle the Gruyere and French-fried onions evenly over the casserole.
  5. Bake for 8 to 10 minutes, until the cheese is melted and the onions are golden.

Notes

For the best texture, pat the thawed green beans dry before adding them to the sauce. Refrigerate leftovers in an airtight container for up to 4 days; freezing is not recommended because the creamy sauce can separate. For a vegetarian variation, use vegetable broth and vegetarian Worcestershire sauce.