Here's what you'll need:
1. Start by removing all the stem ends of the green beans. No need to bust out a knife; just snap 'em off.
2. Then quarter your mushrooms (no need to remove the stems)....
3. ...thinly slice your onions...
4. ..and finely chop your garlic.
5. Add the green beans to a large pot of salted boiling water. Cook them till they’re bright green and tender, about 4 minutes. Drain them and set aside.
This is called ~blanching~ the green beans, and it softens them to make sure they are super tender in the casserole.
6. Heat the olive oil in a large skillet over medium-high heat and add the onions and garlic; season with salt and pepper.
7. Cook the onions till they’re starting to brown and become totally softened, 6-8 minutes. Add the butter and mushrooms and stir so they get all coated in the butter.
8. Once the mushrooms and onions are pretty browned, sprinkle the flour over the the whole thing. Stir this for about 2 minutes, to toast the flour.
9. Add the cream and water, stirring to blend it as you pour.
Cook until the cream has thickened, about a minute, then remove from the heat.
10. Add in the green beans and give them a toss to coat them in all that delicious, creamy mushroom gravy.
Tongs are a helpful tool here, but a spoon works too.
11. Transfer the creamy green beans to an oven safe baking dish or shallow Dutch oven. This can be literally any 2-3 quart baking dish you have, as long as they all fit.
12. HERE COMES MY FAVORITE PART: Sprinkle the whole can of French's Onions over the green beans.
13. Place it in the 425° oven on the top rack (it's cool if there are other things in there, too) and bake until the onions get all brown and crispy, 25-30 minutes.
Green Bean & Mushroom Casserole with Fried Onions
Recipe by Alison Roman
3 lbs. green beans, stemmed
Kosher salt and pepper
2 Tbsp. olive oil
1 large onion, thinly sliced
4 cloves garlic, sliced
4 Tbsp. unsalted butter
1 lb. button mushrooms, quartered
2 Tbsp. all-purpose flour
1 cup heavy cream
¼ cup water
1 (2.8-oz.) package of French's Onions
Preheat the oven to 425°.
Bring a large pot of salted water to a boil and add the green beans. Cook them till they're bright green and tender, about 4 minutes. Drain them and set them aside in a bowl or large plate.
Heat the olive oil in a large skillet over medium-high heat. Add the onion and garlic and season with salt and pepper. Cook the onions till they're starting to brown and become totally softened, 6-8 minutes. Add the butter and mushrooms and season again with salt and pepper. Cook the mushrooms until they're super brown and totally softened (mushrooms are mostly water, so this takes some time), 10-12 minutes. Add the flour and stir to coat all the vegetables. As you cook, the flour will start to brown at the bottom of the skillet— this is what you want!
Add the cream and water and stir, scraping up all the browned bits. Cook until the cream has thickened, about a minute, then remove from heat.
Add the green beans to the skillet and toss to coat everything evenly (if the skillet is too full, you can do this in a bowl).
Transfer to a baking dish. (If you've got an 8x8 baking dish, use that. But any 2-3 quart or an ovenproof skillet works too. ) Top with those wonderful French's Onions.
Bake until top is really brown and crunchy, 25-30 minutes.
You can make this with out the crispy onions part the day before, if you've got the space in your fridge to keep it.
When you're ready to serve, sprinkle with onions and proceed.