-
1
Make the topping: Separate the onion strips and soak in the buttermilk at least 10 minutes.
-
2
Heat 2 inches of vegetable oil in a large pot or Dutch oven over medium heat until a deep-fry thermometer registers 360 degrees F. Combine the flour, panko, parsley and 1 teaspoon salt in a medium bowl.
-
3
Working in batches, remove the onion strips from the buttermilk, dip in the flour mixture and fry until golden brown and crisp, about 3 minutes.
-
4
Transfer to a paper towel-lined plate; season with salt.
-
5
Make the casserole: Bring a large pot of salted water to a boil.
-
6
Add the green beans; cook until crisp-tender, about 6 minutes.
-
7
Drain, rinse under cold water and blot dry with paper towels.
-
8
Preheat the oven to 375 degrees F. Melt the butter in a large pot over medium-high heat.
-
9
Add the mushrooms, season with salt and cook, stirring occasionally, until lightly browned and tender, about 7 minutes.
-
10
Add the garlic and thyme; cook 1 minute.
-
11
Add the flour and stir to coat, 1 minute.
-
12
Whisk in the half-and-half, chicken broth, cayenne and 1/2 teaspoon salt.
-
13
Bring to a simmer and cook, whisking occasionally, until slightly thickened, about 5 minutes.
-
14
Stir in the parmesan and green beans.
-
15
Transfer to a 3-quart baking dish.
-
16
(You can refrigerate the casserole, covered, for up to 4 hours; keep the topping at room temperature.)
-
17
Bake the casserole until bubbling, about 15 minutes.
-
18
Stir, then sprinkle with the topping; bake until warmed through, 5 more minutes.
-
19
Photograph by Ryan Dausch
