Fancy-Up Your 50's-style Green Bean Casserole

Haricot Vert, Carmelized Onion, and Mushroom Gratin

I've always been a fan of classic green bean casserole.  It was one of the first dinner side dishes that my mom let me make all by myself as a kid.  Open two cans of French cut green beans and one can of mushroom soup, stir together with some French fried onions and bake.  It was delicious and I don't care that it was homemade in a Sandra Lee kinda way - I loved it.  I still have a fondness for this canned concoction but my upgraded version takes the dish from kitschy and humble to earthy and ever so slightly more refined. 

Ingredients 

1 bag frozen haricot vert (I like the kind from Trader Joe's)

About 3 cups mushrooms (I like a mix of baby bellas and shitakes here but have used oyster mushrooms in the mix as well)

4 Tbs butter

1 Tbs olive oil

2 Tbs flour

2 cups whole milk

2 tsp truffle oil

1 large yellow onion

a pinch of dried thyme leaves

1 tsp Worcestershire sauce

1 can French fried onions 

The frozen haricot vert taste just as good as fresh in my book, and don't get too watery (unlike many frozen veggies).  You could substitute fresh for frozen but considering that this is a casserole where the beans will be slowly baked in a sauce, it hardly seems worth the trouble to clean them and the extra cost.  Allow them to thaw as you cook the rest of the ingredients so they're easier to incorporate later.

Start by making a roux with 2 Tbs butter and the flour in a saucepan and mix in the milk.  Bring to a bubble, add salt and pepper to taste, then remove from heat.  

In a large frying pan, saute sliced onions with 2 Tbs butter and dried thyme over medium heat. You're going to be caramelizing the onions so watch them closely so they don't burn.  If the pan gets dry add a small splash of water and keep cooking.  This might be cheating but I don't care because it works.  It'll lift some caramelization from the bottom of the pan and the onions will continue to soften and turn sweet.  I find that it takes longer for the onions to caramelize if you salt them, so hold off until the end.  

After 15 minutes or so add in the Worcestershire sauce and add to the pot of white sauce.  If you have an immersion blender, pop it in and blend halfway to flavor the sauce but allow some pieces of onion to remain chunky.

Clean your mushrooms and cut into chunky pieces.  Add to the baking dish that you will be assembling the final casserole in.  Toss with olive oil and a bit of salt and pepper and roast in a 400 degree oven until lightly browned.  

Add haricot vert to the baking dish with the mushrooms and toss with the sauce so everything is evenly coated.  Top with French fried onions (I'm not throwing tradition completely by the wayside!).  You could of course fry your own shallots or thin onion slices, but these really are fantastic so why fight it?

This casserole can be made ahead or heated immediately in a 375 degree oven for 35 minutes or until bubbling.