Green Bean Casserole

On real Thanksgiving my mom always makes Broccoli Bake, the kind using the Campbell's soup, and it's nearly everyone's favorite. Simply to be different for Fakesgiving, we made green bean casserole from scratch. This recipe is a keeper too, but by no means will it be a replacement! It can be easily halved.
Green Bean Casserole
Cooks Illustrated magazine, Nov & Dec 2006

Topping
4 slices white sandwich bread, each torn into quarters
2 T unsalted butter, softened
1/4 t. salt
1/8 t. pepper
3 cups (about 6oz) canned French fried onions

Beans and Sauce
Table salt
2lbs green beans, ends trimmed and halved
3 T. unsalted butter
1lb white mushrooms, stems trimmed, wiped clean, and cut into 1/2 inch pieces (we used crimini mushrooms, or baby bellas, and it gave the dish a stronger mushroom flavor)
3 medium garlic cloves, minced
Pepper
3 T. all-purpose flour
1 1/2 cups low-sodium chicken broth
1 1/2 cups heavy cream

For the topping: Pulse bread, butter, salt, and pepper in a food processor until mixture resembles coarse crumbs, about 10 1-second pulses. Transfer to a large bowl and toss with onions and set aside.

For the beans and sauce: Preheat oven to 425 degrees. Fill a large bowl with ice water. Bring 4 quarts of water to a boil in a large pot, then add 2 T. of salt and the beans. Cook 6 minutes, then drain beans in a colander and plunge immediately into the bowl of ice water. Spread the beans out on paper towels to dry off.

In the now empty large pot, add the butter and melt over med-high heat. Add mushrooms, garlic, 3/4 t. salt, and 1/8 t. pepper, and cook 6 minutes. Add flour and cook 1 minute, stirring constantly. Stir in broth and bring to a simmer, stirring constantly. Add cream, reduce heat to medium, and simmer until sauce is thickened, about 12 minutes. Season with salt and pepper to taste. Add green beans to the sauce and stir to coat. Pour into a 3 quart (or 13x9 inch) baking dish. Add the topping, and bake until top is golden brown and sauce is bubbling around the edges, about 15 minutes. Serve immediately.

Make ahead tip: Combine the beans with the cooled sauce in the baking dish, cover, and refrigerate for up to 24 hours. Store the bread-crumb topping in the fridge and combine with the onions just before cooking. To bake, heat the beans and sauce at 425 for 10 minutes, then add the topping and bake for another 15 minutes.