Serves
6-8 servings
Ingredients
6 tablespoons unsalted butter, divided
1/2 cup all-purpose flour, divided
Kosher salt and freshly ground black pepper
1/2 cup vegetable oil
4 large shallots, thinly sliced into rings
1 medium yellow onion, thinly sliced
2 pound green beans, trimmed
12 ounces cremini or button mushrooms, trimmed and cut into 1/2" slices
2 large garlic cloves, minced
2 cups low-sodium chicken or vegetable broth
1 1/2 cups half and half
Juice from 1 lemon
Procedure
Preheat oven to 400°F and generously grease a 13 x 9" baking dish with butter.
To prepare crispy shallots: To a small bowl, combine 1/4 cup flour, 1/2 teaspoon salt and 1/2 teaspoon pepper. Toss shallots in flour mixture to coat evenly. To a medium skillet set over medium-high heat, add oil. When oil is shimmering, add shallots and cook until browned and crispy, 8-10 minutes. Using a slotted spoon or spider, transfer shallots to a paper towel-lined plate to drain. Sprinkle fried shallots with additional salt. Reserve oil for another use.
To blanch beans: Prepare a large bowl of ice water and set aside. Bring a large pot of water to a rolling boil over high heat. Generously season water with salt. Add beans and cook until crisp-tender, about 2 minutes. Remove green beans from boiling water and transfer to a bowl of ice water; cool and drain well.
To prepare filling: To a large saucepan set over medium-high heat, add 2 tablespoons butter. When foaming subsides, add onion and sauté until softened, about 5 minutes. Add mushrooms and sauté until water is released and mushrooms are browned, about 5 minutes. Add garlic and sauté until fragrant, 1 minute. Season with salt and pepper. Transfer vegetables to a mixing bowl, reserving fat.
Return saucepan to medium-high heat and add remaining 2 tablespoons butter. When butter is melted, whisk in remaining 1/4 cup flour until smooth. Gradually add broth and milk, whisking continuously. Once all liquid is added, bring to a simmer and cook until thickened, about 4 minutes. Season with salt and pepper.
Remove saucepan from heat and fold in green beans, vegetables and lemon juice. Taste and adjust seasoning with additional salt, pepper and lemon juice. Transfer to prepared baking dish and sprinkle crispy shallots over top.
To bake casserole: Transfer casserole to preheated oven and bake until filling is bubbling and topping is browned, 15 to 20 minutes.
