PREHEAT oven to 425ºF. Coat 2-quart baking dish with cooking spray.
BOIL several inches of water in large saucepan fitted with steamer. Add green beans and steam until crisp-tender, about 4 minutes. Carefully remove steamer from saucepan to stop beans from cooking further.
HEAT 4 teaspoons of oil and butter in 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 mushrooms have released their juices and liquid has evaporated, 3 to 4 minutes. Add sherry and cook, stirring occasionally until liquid has evaporated, 2 to 3 minutes.
SPRINKLE flour over mushroom mixture and stir to coat. Add broth and milk and bring to simmer, stirring often, until sauce is thickened, about 5 minutes.
REMOVE from heat and stir in 1½ cups of cheddar. Add green beans and stir to combine. Transfer to prepared dish. Top with remaining ½ cup of cheddar.
STIR together breadcrumbs and remaining ½ teaspoon of oil in a small bowl. Add paprika and onion powder and stir until breadcrumbs are evenly moist and bright orange. Sprinkle over casserole.
BAKE 20 to 25 minutes or until bubbling and golden brown on top. Let cool for about 15 minutes before serving.
Ingredients
Cooking spray
6 cups green beans, trimmed and cut into 1-inch pieces (about 1½ pounds)
4½ teaspoons extra-virgin olive oil, divided
1 tablespoon Cabot Unsalted Butter
3 shallots, minced
8 ounces Cremini or white mushrooms, finely chopped
