Green Bean Casserole

This recipe originally comes from The Mean Green on Food Network.  I made a couple of changes based on recommendations from Chris, who made this for Thanksgiving, and a few more changes based on my personal tastes.  This is by far the best green bean casserole I've ever tasted, and I'll definitely be making it again in the future.  It is a bit time-intensive, but absolutely worth it.

Green Bean Casserole

Ingredients:
For the Beans:

• 1 pound green beans, ends trimmed, cut into 2-inch pieces (weighed prior to trimming)
• 2 strips bacon, cut into 1/2-inch slices
• 1/2 tablespoon olive oil
• 1 large Vidalia sweet onion, 1/2 cut into large dice, 1/2 reserved
• 1 Portobello mushroom
• 1 tablespoon minced shallots
• 1/4 teaspoon salt
• 1/4 teaspoon freshly cracked pepper
• 1/4 teaspoon cayenne pepper

For the Roux:

• 2 Tablespoons butter
• 1/2 cup all-purpose flour
• 1 cup milk
• 1/2 teaspoon freshly cracked black pepper
• 1/2 teaspoon salt
• 1 cup panko bread crumbs

For the Topping:

• 1/2 cup buttermilk
• Reserved 1/2 Vidalia onion, thinly sliced
• 3 medium shallots, thinly sliced
• 1 cup all-purpose flour
• 1 teaspoon granulated garlic
• 1/2 teaspoon dry mustard
• 1/2 teaspoon seasoned salt
• 1 teaspoon freshly cracked black pepper
• 4 cups canola oil

Directions:

1. Preheat oven to 350 degrees F.
2. In a large pot of boiling water, blanch green beans (cook at rolling boil for 2-3 minutes).
3. Remove to an ice bath until cool, drain and let dry.
4. Lightly butter a 9 by 9-inch glass baking dish.
5. In a large frying pan, over medium-high heat, saute bacon until lightly crispy; remove bacon to a paper towel lined plate to drain.
6. In remaining bacon fat, add olive oil, heat over medium-high heat, add onions and saute until just starting to caramelize.
7. Add in mushrooms, garlic and minced shallot and saute for 2 more minutes. Season with the salt, pepper and cayenne. Set aside.
8. In a medium saucepan over medium heat, melt butter. When butter is melted, add in flour, all at once, and stir vigorously with a wooden spoon until well combined. Continue to stir for 1 minute more.
9. Add in milk 1/4 cup at first, stirring well to combine, then add 1/2 cup more milk, stir to combine and bring to a simmer, then add final 1/4 cup of milk and stir and simmer until thickened.
10. Add in seasonings, combine with onion mixture and green beans, and pour into prepared pan. Top with 3/4 cup panko crumbs, then reserved bacon, then remainder of panko lightly sprinkled on top.
11. Place in oven, set timer for 35 minutes.
12. In a medium bowl place buttermilk, onion, and shallots. Let sit 10 minutes, drain well.  
13. In a medium bowl, combine flour and seasonings. When green beans have been in the oven 25 minutes, in a large frying pan, heat canola oil to 350 degrees F.
14. While oil is heating, dredge drained onion and shallots in flour mixture. Drop carefully into the hot oil, 1/3 at a time. They will cook rapidly, 1 minute or less. Turn over if necessary. Remove and drain on paper towels. Let oil heat between batches.
15. When timer goes off for green beans, take out of oven, top with onion-shallot mixture, evenly coating the casserole, place back into oven and continue to cook for 5 more minutes. Remove and let set 5 minutes before serving.

Notes:
I halved everything except the fried onion topping from the original recipe.  I love having tons of crunchy fried onions and shallots on top.  I used peanut oil instead of canola oil, because it's what I happened to have handy.