Crispy Top Green Bean Casserole

Directions

1. 1
   Preheat the oven to 350 degrees F.
2. 2
   (If you haven't steamed your green beans, begin with those they'll be done, about 20 minutes, by the time you need to mix them into the casserole.
3. 3
   ).
4. 4
   Begin the sauce: in a saucepan melt the butter over low heat, then whisk in the flour, stirring continually, and cook for 2 minutes (the mixture will be quite thick).
5. 5
   Gradually add the milk while whisking, and bring to a simmer; cook, whisking continually, for 3 or so minutes and it thickens.
6. 6
   Add the concentrated chicken base, celery salt, nutmeg, and white pepper; whisk well to make sure chicken base is dissolved, remove from heat and set aside.
7. 7
   Begin the filling: in a large nonstick skillet, melt together the olive oil and butter over medium heat; add the onion and garlic, and saute until onion begins to soften, about 5 to 7 minutes.
8. 8
   Add the chopped mild green chiles, stir well to combine, and let the mixture brown for about 3 minutes without stirring.
9. 9
   Add the sliced mushroom, cover, and saute, stirring occasionally, until mushrooms are tender, about 5 minutes; remove about half of the mushroom mixture from the pan and set it aside.
10. 10
    In a 1 1/2 quart lightly-sprayed casserole dish, combine the half of the mushroom mixture from the pan, the cooked green beans, and the white sauce; taste test and adjust salt and pepper, if necessary.
11. 11
    Combine the remaining mushroom mixture with the bread crumbs; combine the melted butter and the sage, then stir it into the crumb mixture.
12. 12
    Spread the crumb mixture over the beans.
13. 13
    Bake uncovered for 30 minutes.