Wild Mushroom Green Bean Casserole

Canned green beans, canned cream of mushroom soup, canned fried onions…don’t get us wrong, green bean casserole is a holiday classic for good reason. But we decided that it was a classic that deserved an upgrade.

Green beans are the star, so treat them accordingly. Fresh green beans are still available in the markets in late fall/winter, and they taste so much better than their canned counterparts. Blanched and shocked, they’re bright green and tender-crisp. Mushrooms and onions, caramelized with a broth made from dried porcini, bring an umami depth. They’re all bound together with a asiago béchamel sauce and topped with buttermilk-brined fried onion strings and dotted with pomegranate seeds that lend bright color and sweet tang.

Of course, you could always use the canned ingredients instead. That is faster to prepare, to be sure. But the extra effort is more than worth it. This is a green bean casserole that’s even great when it isn’t the holidays!

Prep Time: 30 minutes
Cook Time: 1 hour 15 minutes
Total Time: 1 hour 45 minutes
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Serves 15 people


  • 1 oz dried porcini
  • 2 large yellow onions
  • 2 cups buttermilk
  • kosher salt
  • 2 1/2 lbs fresh green beans
  • 4 cloves garlic
  • 1 lb cremini mushrooms
  • 3 tbsp olive oil
  • 6 tbsp unsalted butter
  • 2 1/2 cups all-purpose flour
  • 3 cups milk
  • 2 oz Asiago, shredded optional
  • black pepper
  • 2 tsp baking powder
  • 3 cups vegetable oil
  • 1/2 cup pomegranate seeds


First prep

  • Slice each of the onions in half, then slice again with the cut sides down to make thin (1/8") half-circle slices. Put half the onion slices in a bowl and cover with the buttermilk and refrigerate for 30 minutes. Set the remaining onion slices aside.


  • Bring a large (5-7 quart) pot of water to a boil, and have a large bowl filled with ice water ready in the freezer.
  • While the water is boiling, prep each of the following and set each aside separately. For the green beans, snap the stems off and slice longer beans in half so that you end up with pieces that are about 2-3" long. For the cremini mushrooms, trim off the stem ends and slice the mushrooms 1/4" thick. Mince the garlic.
  • When the water is boiling, remove two cups of the water to a heat-proof bowl or mixing cup. Stir in the dried porcini and let steep for at least 20 minutes.
  • Preheat the oven to 400°F and place a rack in the middle of the oven. Have a 9"x13" casserole dish standing by on the counter.
  • Return to the large pot of boiling water and add 2 tsp salt. Take the bowl of ice water out of the freezer. Add the green beans to the boiling water and cover so that the water comes back to a boil more quickly. Blanch the beans for about 2-4 minutes until bright green and crisp-tender, then remove with a slotted spoon to the ice water to stop the cooking, then drain in a colander and set aside to dry.
  • Line a fine-mesh strainer with a paper towel, then strain and reserve the liquid from the porcini, pressing the mushrooms to release as much liquid as possible. Discard the porcini.
  • Heat the olive oil in a large saute pan over medium high heat. Add the reserved sliced onions as well as the garlic to the pan and toss/stir to coat with the oil. Stir frequently to prevent the garlic from burning. When the onions start to turn translucent, add the sliced cremini mushrooms and toss to distribute. Continue to saute as the mushrooms release their juice and the mushrooms and onions begin to brown.
  • Add the reserved porcini broth to the pan and stir to distribute. Saute until the porcini broth has been fully absorbed and the mushrooms, onions, and garlic are golden brown. Remove from heat and add the mixture to the empty casserole dish.
  • Separate 6 tablespoons of the flour and reserve the rest, keeping the 6 tablespoons nearby for the béchamel sauce.
  • Heat the butter in a medium sauce pan over medium-high heat. When the butter is melted, add the 6 tablespoons of flour and whisk to combine, stirring constantly. When the flour starts to turn light brown, add the milk in a steady stream as you whisk it in. Keep stirring until the béchamel has thickened. Turn off heat. If you're opting to use Asiago, add it now and stir to melt. Add salt and pepper to taste.
  • Add the now-dry green beans to the onion-garlic-mushroom mixture in the casserole dish and pour the béchamel in, stirring gently to coat everything. Bake uncovered for 20-30 minutes until the mixture is bubbling and starting to brown.

Fried Onions

  • While the casserole is baking, take the marinating onions out of the refrigerator and strain out the buttermilk, shaking the onions to get rid of any excess buttermilk. The onions should be damp but no longer soaking.
  • In a 2 quart saucepan, add the vegetable oil and heat on medium until the oil reads approximately 360°F.
  • Using a heavy paper bag, gallon-size sealable plastic bag, or tight-sealing food-safe tub, add reserved flour, baking powder, and 3 tsp salt, seal and shake to combine.
  • Dredge the onions: A handful at a time, take some of the onions, shake off more of the buttermilk, and add the onions to the flour mixture and seal and shake to coat. You can leave the dredged onions in the bag as you add another handful onions to dredge. Repeat until all the onions are dredged.
  • Gently add a handful of dredged onions to the hot oil. It will bubble up a bit and then subside. Fry, stirring occasionally, for about five minutes until the onions are deep golden brown, then remove with tongs to a cooling rack set on top of paper towels. Repeat, a handful of onions at a time, until all the onions are fried. Add additional salt (and/or fresh ground black pepper if desired) to the fried onions to taste.
  • Let onions cool completely and store in an airtight container until just before serving.


  • If bringing to the party right away, keep the casserole warm from the oven and top with the onions and pomegranate seeds just before serving. If making ahead, wait to bake and refrigerate the assembled casserole until an hour before you need to leave. Bake and serve as directed.


Calories: 235kcal | Carbohydrates: 29g | Protein: 8g | Fat: 11g | Saturated Fat: 5g | Cholesterol: 20mg | Sodium: 93mg | Potassium: 508mg | Fiber: 3g | Sugar: 7g | Vitamin A: 772IU | Vitamin C: 11mg | Calcium: 168mg | Iron: 2mg

Kids’ Table

Does your young chef want to help out? Here are some suggestions of ways they can contribute, based on their skill level.


Pick through and snap the green beans, plus do the bag-shaking part of breading the onions


Help with vegetable prep and assemble and bake the casserole, with adult supervision


Blanch/shock the green beans, caramelize onions and mushrooms, and fry onions, with adult supervision

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