Ingredients

For the Topping

• 4 slices white bread, each slice torn into quarters
• 2 tablespoons (28 g) unsalted butter, softened
• ¼ teaspoon salt
• ⅛ teaspoon ground black pepper
• 6 oz canned fried onions

For the Beans and Sauce

• 2 tablespoons salt, for cooking water
• 2 pounds green beans, ends trimmed, and halved*
• 3 tablespoons (43 g) unsalted butter
• 1 pound white button mushrooms, stems removed, wiped clean and broken into ½-inch pieces
• 3 cloves garlic, minced
• ¾ teaspoon salt
• ⅛ teaspoon ground black pepper
• 3 tablespoons all-purpose flour
• 1½ cups (360 ml) chicken broth
• 1½ cups (360 ml) heavy cream

Instructions

1. For the Topping: Pulse bread, butter, salt and pepper in food processor until mixture resembles coarse crumbs, about ten 1-second pulses. Transfer to a large bowl and toss with onions; set aside.
2. For the Beans and Sauce: Preheat oven to 425 degrees F. Fill a large bowl with ice water. Bring 4 quarts of water to a boil in a large pot or Dutch oven. Add 2 tablespoons salt and the beans. Cook the beans until bright green and crisp-tender, about 6 minutes. Drain beans in colander and plunge immediately into ice water to stop cooking. Spread beans on paper towel-lined baking sheet to drain.
3. Add butter to now-empty pot and melt over medium-high heat. Add mushrooms, garlic, salt, and pepper; cook until mushrooms release moisture and liquid evaporates, about 6 minutes. Add flour and cook for 1 minute, stirring constantly. Stir in broth and bring to simmer, stirring constantly. Add cream, reduce heat to medium, and simmer until sauce is thickened and reduced to 3½ cups, about 12 minutes. Season with salt and pepper to taste.
4. Add green beans to sauce and stir until evenly coated. Arrange in an even layer in a 9×13-inch baking dish. Sprinkle evenly with the topping and bake until top is golden brown and sauce is bubbling around edges, about 15 minutes. Serve immediately. Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.

*Frozen green beans may be substitued for fresh green beans