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Ingredients
Scale
- 4 medium yellow onions, halved lengthwise and thinly sliced
- 5 tablespoons unsalted butter, divided
- 2 teaspoons kosher salt, divided
- 1 teaspoon ground black pepper, divided
- 2 ½ pounds green beans, trimmed and cut into 1 ½-inch pieces
- 8 ounces baby bella mushrooms, sliced
- 2 tablespoons all-purpose flour
- 2 ½ cups 2% milk (plus additional as needed)
- ⅛ teaspoon ground nutmeg
- 1 cup croutons, crushed
- ¼ cup freshly grated Parmesan cheese
- 1 ½ cups shredded Gruyere cheese, divided
Instructions
- Caramelize the onions with butter, salt, and pepper for 90-120 minutes until golden brown.
- Preheat oven to 375°F and prepare green beans by boiling, then shocking in an ice bath.
- Sauté mushrooms in remaining butter, add flour, and cook until golden.
- Gradually incorporate milk into the mushroom mix, thickening the sauce.
- Layer green beans, sauce, onions, and Gruyere cheese in a casserole dish.
- Top with a mixture of croutons, Parmesan, and melted butter.
- Bake for 25-30 minutes until bubbly and golden brown.
Notes
Patience is essential while caramelizing onions for optimal flavor.
For a vegetarian version, omit meat and use vegetable broth.
This dish can be prepared a day ahead and baked before serving.
- Prep Time: 30 minutes
- Cook Time: 2 hours
- Category: Side Dish
- Method: Baking
- Cuisine: French
Nutrition
- Calories: 320
- Sugar: 5
- Sodium: 450
- Fat: 18
- Saturated Fat: 10
- Unsaturated Fat: 5
- Trans Fat: 0
- Carbohydrates: 30
- Fiber: 4
- Protein: 8
- Cholesterol: 35