Thanksgiving Side Dishes: Green Bean Casserole with Crispy Onions
By Emily Carter ·
Published
Quick answer
Blanch 2 pounds of trimmed green beans until bright green and just tender, fold into a homemade creamy mushroom sauce built on butter, cremini mushrooms, milk and sour cream, spread in a 9x13 inch dish, top with crispy fried onions and bake at 350 degrees F until bubbly and golden. Assembles in about 50 minutes plus a 5 minute rest, and you can build it a full day ahead.
Thanksgiving side dishes are the dishes people fight over seconds of, and this green bean casserole earns its place on the table. Fresh green beans blanched bright green, folded into a from scratch creamy mushroom sauce with sour cream, and finished with a golden layer of crispy fried onions. It tastes like the classic you grew up with, only better, and it assembles a full day ahead so the big day stays calm.
Why you’ll love it
- A from scratch mushroom sauce that beats the canned soup version on flavor and texture.
- Make ahead friendly: assemble a day early and bake when guests arrive.
- Crispy fried onions stay crisp because they go on right before baking.
- Serves a crowd: one 9x13 inch dish feeds about 10 people.
- Vegetarian and easy to adapt to what is in the pantry.
Ingredient notes
Fresh green beans: the star of the dish. Look for firm, bright beans that snap cleanly. A quick blanch keeps them green and just tender so they do not turn mushy in the oven.
Cremini mushrooms: they give the sauce real depth. Sliced mushrooms cooked until golden add the savory flavor that canned soup tries to imitate. White button mushrooms work too, with a milder result.
Sour cream: stirred in off the strongest heat, it adds tang and body. It is what keeps a rich butter and milk sauce from tasting one note.
Crispy fried onions: the classic crunchy crown. Store bought fried onions are the right call here for crunch and convenience. Keep them in the pantry until baking time.
Nutmeg: just a quarter teaspoon of freshly grated nutmeg. It is the quiet background note that makes creamy sauces taste complete.
The blanch that keeps the beans bright green
Two minutes of prep on the beans pays off in the final dish. Blanching in well salted boiling water sets the bright green color and takes the raw edge off, while shocking in cold water stops the cooking fast. Beans that go into the casserole raw turn olive and rubbery; beans that go in overcooked turn to mush. Four to five minutes is the sweet spot: tender with a little bite. The other half of the trick is drying them. Water clinging to the beans is the number one cause of a thin, watery casserole, so pat them down with a kitchen towel before they meet the sauce.
Variations
- Extra cheesy: fold 1 cup of shredded sharp cheddar into the sauce with the sour cream for a richer, kid friendly version.
- Mushroom forward: double the cremini mushrooms to 16 ounces and skip half the beans for a sauce heavy bake.
- Gently spiced: add 1/4 teaspoon of cayenne to the sauce for a warm background heat that suits a big holiday table.
- Gluten free: swap the all purpose flour for an equal amount of cornstarch whisked into the cold milk, and use a gluten free crispy onion topping.
What we learned testing it
- Blanching beat roasting in the side by side test. Roasted beans turned olive and shriveled, while blanched beans stayed bright green with a fresh bite.
- Whole milk made a noticeably creamier sauce than low fat milk, and the sour cream at the end added the tang that keeps a rich casserole from tasting flat.
Read how we test recipes.
Thanksgiving Side Dishes: Green Bean Casserole with Crispy Onions
Makes 1 9x13 inch casserole (about 10 servings) · 55 min total · Easy
Ingredients
Equipment
9x13 inch baking dish · Large pot · Colander · Large skillet · Large mixing bowl · Wooden spoon
Instructions
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Blanch the green beans until bright green
Bring a large pot of salted water to a rolling boil. Add the green beans and cook for 4 to 5 minutes until bright green and just tender with a little bite left. Drain in a colander and run under cold water to stop the cooking. Spread the beans on a clean kitchen towel and pat them dry so the sauce clings later.
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Build the creamy mushroom sauce
Melt the butter in a large skillet over medium heat. Add the mushrooms and onion and cook for 6 to 8 minutes until golden and soft. Stir in the garlic and cook 1 minute more. Sprinkle in the flour and stir for 1 full minute, then slowly whisk in the milk and vegetable broth. Simmer for 3 to 4 minutes until thickened, then stir in the sour cream, salt, pepper and nutmeg. Taste and adjust the seasoning.
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Combine and fill the baking dish
Heat the oven to 350 degrees F. Fold the blanched green beans into the sauce in a large bowl until every bean is coated. Spread the mixture evenly into the baking dish and smooth the top. At this point you can cover and refrigerate the unbaked casserole for up to 24 hours.
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Top with crispy onions and bake
Scatter the crispy fried onions evenly over the top. Bake for 30 to 35 minutes until the sauce is bubbly around the edges and the onions are deep golden. Let the casserole rest for 5 minutes so the sauce sets, then serve hot straight from the dish.
Notes
- Dry the beans well after blanching. Water on the beans thins the sauce and makes the casserole watery instead of creamy.
- Do not skip the flour cooking step. One full minute of stirring cooks out the raw flour taste before the milk goes in.
- Add the onion topping right before baking. Onions added too early or placed on a refrigerated casserole can soften in the fridge.
- Let it rest. Five minutes on the counter lets the sauce thicken into a proper creamy casserole instead of a loose bake.
Nutrition per serving
Nutrition information is being calculated.
Substitutions
- Fresh green beans
- Use 2 pounds of frozen whole green beans, thawed and patted very dry. Skip the blanching and fold them straight into the sauce, but dry them well or the sauce will thin.
- Cremini mushrooms
- Use white button mushrooms instead. The sauce will be a touch milder, so add an extra pinch of salt at the end to bring the flavor back.
- Sour cream
- Use plain Greek yogurt instead. Whisk it smooth before stirring in so it melts into the sauce without curdling, and expect a slightly tangier finish.
Storage and make-ahead
Cool the casserole completely, then cover and refrigerate for up to 4 days. Reheat covered at 325 degrees F for 20 to 25 minutes until hot in the center, adding a fresh handful of crispy onions on top for the last 5 minutes. Freeze the unbaked casserole without the onion topping for up to 2 months; thaw overnight in the fridge, top with onions and bake as directed.
Frequently asked questions
Can I make this green bean casserole a day ahead?
Yes, that is the whole point. Assemble the beans and sauce in the dish, cover and refrigerate for up to 24 hours. Add the crispy fried onions right before baking and add 5 to 10 minutes to the bake time since it starts cold.
Can I use canned green beans instead of fresh?
You can, but expect a softer, less vibrant casserole. Drain two 14.5 oz cans very well and skip the blanching. Fresh beans stay greener and firmer, which is the main reason this version tastes better.
Why is my green bean casserole watery?
The usual cause is wet beans or an undercooked sauce. Pat the blanched beans dry, cook the flour a full minute, and simmer the sauce until it coats a spoon before adding the beans.
Can I make this casserole dairy free?
Yes. Use olive oil instead of butter, unsweetened oat milk instead of whole milk, and a dairy free sour cream alternative. The sauce will be a little less rich but still creamy.
How do I keep the crispy onions from getting soggy?
Add them right before the dish goes into the oven, never before refrigerating. If you are reheating leftovers, add a fresh handful of crispy onions for the last 5 minutes of the reheat.
