Sourdough Green Bean Casserole

I can’t wait for you to try my sourdough green bean casserole – you’re going to absolutely love the fantastic flavor! There’s a rich and savory mushroom gravy made with sourdough discard, crisp-tender green beans, and best of all, oven-baked crispy onions made with sourdough breadcrumbs and discard. After making this, I’ve found myself craving green beans on a regular basis – and even my kids were willing to eat green beans so you know it’s good!

Ingredients

• Green Beans – I prefer this with fresh green beans, but frozen beans work well too! If you opt for frozen, I recommend simmering them in chicken stock (I used two bouillon cubes) until tender. It boosts the flavor a bit more! I personally don’t love the texture of canned green beans, but they will work as a substitute in a pinch.
• Butter – I always use salted butter, but feel free to use whatever you have. You’ll need some for the gravy base, some for the topping, and a bit extra to grease the baking dish.
• Chopped Mushrooms – I’ve used easy-to-get, budget-friendly brown mushrooms here, but feel free to use whatever kind you like or a mix.
• Garlic – I like fresh garlic in this recipe, but you can substitute with garlic powder or granules as well.
• Sourdough Starter or Discard – Either one will work in this recipe. You’ll need some for both the mushroom gravy and the onion topping. I don’t recommend using thick starter here as it can be hard to blend it into a gravy.
• Chicken Stock – I usually make this with a chicken stock cube/bouillon cube unless I happen to have chicken stock already made. Feel free to use any kind of meat or vegetable stock cube, or homemade if you have it.
• Milk – I prefer the richness of whole milk here.
• Salt and black pepper
• Ground nutmeg – Just a pinch helps to flavor the gravy.
• Worcestershire or soy sauce – I like a splash of each to add depth of flavor to my gravies, but if you don’t have one you could add a bit more of the other.
• Red wine vinegar or cider vinegar (optional) – a small splash of vinegar is nice to brighten up the mushroom gravy a bit, but feel free to use any vinegar you have or leave it out. 
• Bread Crumbs – I like to whizz up homemade sourdough in the food processor whenever possible, but store-bought breadcrumbs are a great alternative, especially panko if you can find it. 
• Onion – I used a regular yellow/brown onion here, but any onion or even shallots would work. If you don’t want to make the baked onion topping, store-bought fried onions are a great alternative! Swap in about 2 cups of fried onions in for the sourdough onion-breadcrumb topping, about ⅔ of a cup within the casserole and the remainder scattered on top.
• Egg – I used one large egg to bind the onion topping. 
• Parmesan – I recommend grating your own for the best flavor if you can. 

How To Make Sourdough Green Bean Casserole

You’re going to start by making the sourdough baked onions. Line a baking sheet with parchment paper and preheat the oven to 350ºF/180ºC. Whisk the sourdough starter, egg, melted butter, and salt in a small bowl, setting this aside. In a wide dish, mix the the breadcrumbs and Parmesan together, ready to dredge the onions.

Use tongs or your hands to coat some onions in the sourdough-egg mixture, then dredge them in the breadcrumbs and Parmesan. Place the crispy onions on the prepared baking sheet and continue until all the onions are done. Don’t worry about trying to perfectly coat the onions  – I love how it tastes when the sourdough breadcrumbs and onions clump up and make for delicious rustic craggy bits!

Place in the oven and bake for 10 minutes. Use a spatula to flip the onions and bake for another 10 to 15 minutes, until golden brown and crispy on all sides. Set aside until the casserole components are ready.

Next, you’ll prepare the green beans. Bring a large pot of well-salted water to a boil with an ice bath nearby. Once the water is boiling, add the green beans and cook for 4 to 5 minutes, until tender but still crisp and green. You don’t want to overcook them, or they’ll turn a muddy brown-ish green. Strain and transfer beans to the ice bath. Once the beans are chilled, drain and set aside.

Next, you’ll make the mushroom gravy by melting the butter over medium-high heat in a medium saucepan. I like to chop mushrooms in the food processor because it’s super easy and makes them small enough that you can easily whisk up the gravy. But only give it a few pulses so you have some chunky bits of mushroom to give the gravy some texture. If you prefer sliced, you can do that too. 

Depending on the type of mushrooms, they can release quite a lot of liquid, so you need to cook the chopped mushrooms until they start to brown. You want all this liquid to cook off to get the most flavor out of the mushrooms, which takes about 8 to 10 minutes. It should smell really good and mushroomy! Once the liquid is gone, add the minced garlic and salt, stir, and cook until the garlic softens a bit, about 2 minutes.

Add the sourdough starter and stir to coat the mushrooms. Cook for around 2 minutes – the starter will likely catch on the bottom of the pan and start to brown. Don’t worry, this will add lots of flavor! Gradually add the stock, stirring and scraping up the browned bits from the bottom of the pan with a wooden spoon. Add the milk and bring to a simmer, stirring all the while.

Once the mixture is bubbling, turn the heat down to medium and continue to stir for around 6 to 8 minutes. The sauce should be thick and creamy and coat the back of a spoon. Remove from heat and add the vinegar, Worcestershire sauce, soy sauce, black pepper, and nutmeg.

I can’t get enough of this sourdough mushroom gravy with the Worcestershire, soy sauce, and vinegar, plus a bit of nutmeg and black pepper. I always recommend tasting and adjusting as your ingredients might be slightly different from mine, and so you can make it taste just the way you want it! 

Now it’s time to assemble the casserole using a greased 9” x 13” baking dish. You’ll need to add ⅓ of the baked sourdough onions to the green beans, stirring lightly to ensure everything is well spread out. Pour the mushroom gravy on top and stir until the vegetables are evenly coated. Then add the rest of the onion topping to top of the casserole.

Bake the casserole for about 20 minutes, until the sourdough mushroom gravy is piping hot and bubbling, and the top is a crunchy dark golden brown.

How To Serve Sourdough Green Bean Casserole

This green bean casserole deserves a place on your holiday table. I love serving it for Thanksgiving or Christmas alongside roast turkey or ham, homemade sourdough dinner rolls, and plenty of sourdough gravy. Add a pan of sourdough mac and cheese for the ultimate comfort food feast, then finish the meal with a slice of sourdough pumpkin pie for dessert.

Don’t save this recipe just for the holidays though! You can easily halve the recipe and serve it alongside a roast chicken or roast beef for an easy family dinner. It’s a simple way to make an ordinary weeknight meal feel a little extra special.

How To Store + Freeze

This sourdough green bean casserole will keep in the fridge for a few days, well-wrapped.

You can reheat in the oven or the microwave, although the texture of the topping is best in the oven.  This casserole doesn’t freeze well once baked, but you can make it in advance and then refrigerate or freeze.

If you’d like to make this green bean casserole in advance, prepare the beans and mushroom gravy and mix in the casserole dish, then wrap well. You can then refrigerate for two days or freeze for up to three months.

To finish the dish, thaw in the refrigerator if necessary and make the sourdough onion-breadcrumb topping separately, then assemble and bake.

Share the sourdough love!