Green Beans with Cremini Mushroom Sauce

• MAKE-AHEAD

Ingredients

1. 1 pound shallots, thinly sliced
2. 1/3 cup plus 3 tablespoons all-purpose flour
3. Vegetable oil, for frying
4. Salt
5. 2 1/2 pounds green beans
6. 2 tablespoons unsalted butter
7. 1 medium onion, thinly sliced
8. 1/2 teaspoon paprika
9. Pinch of cayenne pepper
10. Freshly ground pepper
11. 1 pound cremini mushrooms, stems discarded, caps thinly sliced
12. 2 cups chicken stock or canned low-sodium broth
13. 1/2 cup crème fraîche
14. 2 tablespoons fresh lemon juice

1. On a large rimmed baking sheet, toss the shallots with 1/3 cup of the flour; shake off any excess flour. In a large, deep skillet, heat 1 inch of oil until shimmering. Add the shallots in 2 batches and fry over moderate heat until very crisp, about 3 minutes. Using a slotted spoon, transfer to paper towels, then sprinkle with salt.
2. In a large pot of boiling salted water, cook the beans until just tender, about 5 minutes. Drain and refresh under cold running water; drain and pat dry.
3. Melt the butter in a large, enameled cast-iron casserole. Add the onion and cook over low heat, stirring occasionally, until softened, about 5 minutes. Add the paprika, cayenne and a large pinch of pepper; cook for 1 minute, stirring. Add the mushrooms, cover and cook over moderate heat until softened, about 5 minutes. Uncover and cook, stirring, until browned, about 5 minutes longer. Stir in the remaining 3 tablespoons of flour and gradually stir in the stock until smooth.
4. Simmer the mushroom sauce over low heat, stirring, until thickened, about 5 minutes. Stir in the crème fraîche, lemon juice and beans. Cover and simmer, stirring occasionally, until the beans are heated through, about 5 minutes. Season with salt and pepper and transfer to a large glass or ceramic baking dish.
5. Preheat the oven to 400°. Cover the casserole with foil and bake until bubbling, about 20 minutes. Uncover, scatter the shallots on top and serve.