Nonstick cooking spray
pounds haricots verts or French green beans, trimmed and cut into 1-inch pieces
pound hen of the woods mushrooms (or cremini, oyster or other mushroom), cut into bite-size pieces
large shallots, halved lengthwise and thinly sliced into half-moons
garlic cloves, minced
tablespoons extra-virgin olive oil
Kosher salt and black pepper
tablespoons unsalted butter
tablespoons all-purpose flour
quart heavy cream or half-and-half
teaspoon Cajun seasoning
teaspoon onion powder
teaspoon garlic powder
teaspoon chicken base concentrate (or 1/2 bouillon cube)
teaspoon ground nutmeg
cups shredded or grated Parmesan
cup panko bread crumbs
cups store-bought or homemade fried shallots or onions
- Heat oven to 400 degrees. Coat a 9-by-13 baking dish with nonstick cooking spray. On a rimmed sheet pan lined with parchment paper, toss together green beans, mushrooms, sliced shallots, garlic and olive oil; season with salt and pepper to taste then spread evenly on the pan. Roast until the vegetables brown in spots and soften, about 30 minutes, tossing halfway through. (Alternatively, if you want the green beans extra soft, set them on an unlined sheet pan, add 3 tablespoons water, cover with aluminum foil, and cook until the vegetables are slightly firmer than you want in the end result, about 30 to 45 minutes.)
- Meanwhile, in a large saucepan over medium-low heat, melt the butter, then add the flour. Cook for about 1 to 2 minutes, whisking constantly until it comes together and begins to turn golden in color.
- Add heavy cream and whisk until it starts to thicken, 6 to 8 minutes. Add the Cajun seasoning, onion and garlic powders, chicken base, nutmeg and 1/2 teaspoon pepper. Whisk to combine, then add 1 1/2 cups Parmesan until melted. Taste and adjust seasonings.
- When the green beans are cooked, add them to the saucepan, and toss to coat until mixture is thoroughly heated. Transfer green bean mixture to the baking dish.
- In a medium bowl, combine bread crumbs, fried shallots and the remaining 1/4 cup Parmesan. Spread evenly over the top of the casserole.
- Set the broiler to high, and broil until brown and bubbly (don’t walk away!), about 1 to 2 minutes. Serve hot.