Homemade Green Bean Casserole

1. Preheat the oven to 375°F. Lightly grease a 9 × 11-inch baking dish.

2. In a large bowl, combine the onion slices, cornstarch, and seasoned salt and toss until the onions are well coated.

3. Pour 3 inches of oil into a deep medium saucepan. Have ready a wire rack lined with paper towels to use for draining . Heat the oil to 350°F on a deep-fry thermometer.

4. Working in batches, use a slotted spoon to lower half the onions into the hot oil. Cook, stirring occasionally, until golden, 2 to 3 minutes. Use a slotted spoon to remove the onions to the paper towel-lined rack. Repeat to fry the remaining onions. Set aside.

5. In a small bowl, mix 1 tablespoon of the butter and the panko. Set aside.

6. Set up a large bowl of ice and water. Bring a large pot of water with 1 tablespoon of the salt to a boil over medium-high heat. Add the green beans and cook until crisp-tender, about 6 minutes. Using tongs, carefully remove the green beans to the ice water to stop the cooking process. Cool in the ice water for 1 to 2 minutes, then drain the beans. Set aside.

7. In a large skillet, heat the remaining 4 tablespoons butter over medium-high heat. Add the mushrooms and cook, stirring frequently, until golden brown, 2 to 3 minutes. Add the remaining 1 teaspoon salt, the pepper, garlic, and nutmeg and stir to combine.

8. Sprinkle the flour over the mushrooms and stir to combine well. Slowly whisk in the chicken broth, bring to a simmer, and cook until well incorporated, about 2 minutes. Reduce the heat to medium and slowly whisk in the cream, stirring until the sauce thickens, 4 to 6 minutes. Remove from the heat and stir in the green beans. Pour into the prepared baking dish and top with the buttered panko.

9. Transfer to the oven and bake until bubbling, 15 to 20 minutes. Top with the fried onions and serve.

10. Store in an airtight container in the refrigerator for up to 2 days.