kosher salt and black pepper
green beans, trimmed and halved crosswise
(1 stick) unsalted butter
button mushrooms, trimmed and quartered
plus 2 tablespoons all-purpose flour
low-sodium chicken broth
shallots, sliced into thin rounds
- Heat oven to 350° F. Bring a large pot of water to a boil; add 1 tablespoon salt. Add the green beans and cook until just tender, 3 to 5 minutes. Drain and transfer to a shallow 2-quart baking dish.
- Heat 3 tablespoons of the butter in a large skillet over medium-high. Add the mushrooms, season with ¼ teaspoon salt and ⅛ teaspoon pepper, and cook, tossing occasionally, until golden brown and tender, 8 to 10 minutes; transfer to a bowl.
- Reduce heat to medium and melt the remaining 5 tablespoons of butter. Add ½ cup flour and cook, stirring, for 1 minute (do not let darken). Whisk in the broth, cream, and ¼ teaspoon salt; bring to a boil and boil and cook for 1 minute. Add the mushrooms to the sauce and stir to combine.
- Pour the sauce over the green beans in the baking dish, cover dish with foil, and bake until bubbly, 30 to 45 minutes.
- Meanwhile, in a small bowl, toss the shallots with the remaining 2 tablespoons of flour. Heat the oil in a medium skillet over medium heat. Cook the shallots, stirring, until golden brown, 6 to 8 minutes; transfer to a paper towel-lined plate and sprinkle with ¼ teaspoon salt. Sprinkle over the beans before serving.