simmer, and cook, whisking, until the mixture has a
consistency somewhere between pancake batter and
heavy cream, about 5 minutes. Season to taste with salt
and pepper and set aside.
Adjust an oven rack to the lower-middle position and
preheat the oven to 350°F. Bring 4 quarts water and ¼
cup kosher salt to boil in a Dutch oven over high heat.
Fill a large bowl with 4 cups ice cubes and 2 quarts
water. Add the green beans to the boiling water and cook
until tender but still green, about 7 minutes. Drain and
immediately transfer to the ice water to cool completely;
drain well.
- Combine the green beans, mushroom sauce, and 1 cup
of the fried shallots in a bowl. Transfer to a 9-by-13-inch
rectangular casserole or 10-by-14-inch oval casserole.
Bake until hot and bubbly, 15 to 20 minutes. Top with
the remaining fried shallots and serve.