- 6 cups green beans, trimmed and cut into 1-inch pieces (about 1 ½ pounds)
- 4 ½ teaspoons extra-virgin olive oil, divided
- 1 tablespoon unsalted butter
- 3 shallots, minced
- 8-ounces Crimini or white mushrooms, finely chopped
- 2 teaspoons chopped fresh thyme
- ½ teaspoon salt
- ¼ teaspoon pepper
- ¼ cup dry sherry
- 1/3 cup all-purpose flour
- 1 cup reduced-sodium chicken broth or vegetable broth
- 1 cup whole milk
- 2 cups sharp cheddar, shredded and divided, 8-ounces
- 3 tablespoons dry breadcrumbs
- ½ teaspoon paprika
- ¼ teaspoon onion powder
- Preheat oven to 425 degrees F. Coat a 2 1/2 quart baking dish with cooking spray.
- Meanwhile, bring several inches of water to a boil in a large saucepan fitted with a steamer basket. Steam green beans until crisp tender, about 4 minutes. Carefully remove steamer from the saucepan, to stop the beans from cooking further.
- Heat 4 teaspoons oil and butter in a large skillet over medium-high heat. Add shallots and cook until just starting to brown, 2 to 3 minutes. Add mushrooms, thyme, salt and pepper and cook, stirring occasionally until the mushrooms have released their juices and the liquid has evaporated, 3 to 4 minutes. Add sherry and cook, stirring occasionally until the liquid has evaporated, 2 to 3 minutes.
- Sprinkle flour over the mushroom mixture and stir to coat. Add broth and milk and bring to a simmer stirring often until the sauce is thickened, about 5 minutes. Remove from the heat and stir in 1 ½ cups (6-ounces) cheddar. Add the green beans and stir to combine. Transfer to the prepared casserole dish. Top with the remaining 1/2 cups (2-ounces) cheddar.
- Stir together the breadcrumbs and the remaining ½ teaspoon oil in a small dish. Add paprika and onion powder and stir until the breadcrumbs are evenly moist and bright orange. Sprinkle over the casserole.
- Transfer the casserole to the oven and bake until bubbling and golden brown on top, 20 to 25 minutes. Allow to cool 15 minutes before serving.