The best green bean casserole ever

Ingredients:

Topping

• 2 medium onions, thinly sliced
• 1/4 cup premium flour
• 2 tbsp. panko breadcrumbs
• 1 teaspoon coarse salt

Green beans and sauce

• 2 tbsp + 1 tsp coarse salt, divided
• 450 g fresh green beans, washed, trimmed and cut in half
• 2 tablespoons unsalted butter
• 340 g mushrooms, trimmed and cut into 1 cm pieces.
• 0.5 tsp ground black pepper
• 2 cloves garlic, crushed
• 1/4 tsp. freshly ground nutmeg
• 2 tbsp. premium flour
• 1 cup chicken broth
• 1 cup light cream

Preparation:

1. Preheat oven to 245°C.
2. Combine the onion, flour, breadcrumbs, and salt in a large bowl. Spray a baking sheet with cooking spray and spread the onions evenly over the sheet. Place the baking sheet on the middle rack of the oven and roast the onions until golden brown, about 30 minutes. Stir 2-3 times during baking. Then remove from the oven and set aside until ready to use. Reduce the oven temperature to 200°C (400°F).
3. While the onions are roasting, prepare the beans. Pour 4 liters of water into an 8-quart saucepan, add 2 tablespoons of salt, and bring to a boil. Add the beans and blanch for 5 minutes. Drain the beans in a colander and immediately transfer them to a large bowl of ice water to stop the cooking. Drain and set the beans aside.
4. In a 12-inch cast-iron skillet, melt the butter over medium-high heat. Add the mushrooms, 1 teaspoon salt, and pepper. Cook, stirring occasionally, until the mushrooms begin to release some of their liquid, about 4-5 minutes. Add the garlic and nutmeg and continue to cook for another 1-2 minutes. Sprinkle the mushrooms with flour and toss. Cook for 1 minute. Add the broth and simmer for 1 minute. Reduce the heat to medium and add the cream. Cook, stirring occasionally, until the mixture thickens, about 6-8 minutes.
5. Remove from heat and stir in 1/4 of the onion and all of the green beans. Sprinkle with the remaining onion. Place in the oven and bake until bubbly, about 15 minutes. Remove from the oven and serve immediately.