thankfully, someone at Chowhound had already typed it out (phew)
Green Bean Casserole, serves 10-12
From "Cooks Illustrated" November & December 2006 issue
4 slices white sandwich bread, each torn into quarters
2 Tbsp. unsalted butter, softened
1/4 tsp. table salt
1/8 tsp. ground black pepper
3 cups canned fried onions (6 oz, about one can)
Beans and Sauce:
2 pounds green beans, ends trimmed, and halved
3 Tbsp. unsalted butter
1 pound white button mushrooms, stems trimmed, wiped clean, and broken into 1/2 inch ieces
3 medium garlic cloves, minced or pressed (1 Tbsp)
Ground black pepper
3 Tbsp. all-purpose flour
1.5 cups low-sodium chicken broth
1.5 cups heavy cream
1. For the topping: Pulse bread, butter, salt & pepper in a food processor until mixture resembles coarse crumbs, about ten 1-second pulses. Transfer to large bowl and toss with onions; set aside.
2. For the beans and sauce: Adjust oven rack to middle position and heat oven to 425 degrees. Fill large bowl with ice water. Bring 4 quarts water to boil in large Dutch oven. Add 2 Tbsp. of table salt, and the beans. Cook beans until bright green and crisp-tender, about 6 minutes. Drain beans in colander and plunge immediately into ice water to stop cooking. Spread beans on paper-towel-lined baking sheet to drain.
3. Add butter to now-empty Dutch oven and melt over medium-high heat until foaming subsides. Add mushrooms, garlic, 3/4 tsp. salt, and 1/8 tsp. pepper; cook until mushrooms release moisture and liquid evaporates, about 6 minutes. Add flour and cook for 1 minute, stirring constantly. Stir in broth and bring to simmer, stirring constantly. Add cream, reduce heat to medium, and simmer until sauce is thickened and reduced to 3.5 cups, about 12 minutes. Season with salt and pepper to taste.
4. Add green beans to sauce and stir until evenly coated. Arrange in even layer in 3-quart (or 13x9-inch) baking dish. Sprinkle with topping and bake until top is golden brown and sauce is bubbling around edges, about 15 minutes. Serve immediately.
and a tweak on the Cooks Illustrated version (looks quite good as well)