How to Make It
Preheat broiler to high.
Cook beans in a large saucepan filled with boiling water 3 minutes or until crisp-tender. Plunge beans into ice water; drain well.
Place bread in a food processor; pulse until coarse crumbs form. Stir in parsley, 1 tablespoon oil, garlic, and 2 tablespoons cheese.
Heat remaining 2 tablespoons oil in a 10-inch cast-iron skillet over medium. Add onion and mushrooms; sauté 8 minutes. Stir in flour; cook 1 minute. Stir in stock, milk, and sherry. Bring to a simmer; cook 3 minutes. Remove pan from heat; stir in remaining 4 tablespoons cheese, salt, pepper, and nutmeg. Add beans to pan; toss to coat. Sprinkle evenly with breadcrumb mixture. Broil 2 minutes.