Intro
Hi, I am Dulcia. This is my best-ever green bean casserole with mushrooms, a creamy, make-ahead side that is perfect for holiday tables or weeknight dinners. I walk you through every step in my step-by-step video so you can get golden mushrooms, a silky béchamel, and crispy fried onions every time.
Watch the video at the top of the post, and read on for notes and variations.
Origins
Green bean casserole is a classic American side, often credited to the 1950s convenience-food movement. For history, see the Wikipedia entry on green bean casserole. This version swaps canned soup for a homemade béchamel and adds deeply browned crimini mushrooms for savory depth. For food safety and storage guidance, I also reference USDA recommendations.
Ingredients
- 2 lb. fresh green beans
- Kosher salt
- 2 Tbsp. extra-virgin olive oil, divided
- 1 lb. crimini mushrooms, sliced, divided
- 6 Tbsp. unsalted butter, divided
- 4 large sprigs thyme, divided
- 2 Tbsp. all-purpose flour
- 1¼ cups whole milk
- 1 cup heavy cream
- 4 garlic cloves, finely grated
- ½ cup grated Parmesan
- Freshly ground black pepper
- ¾ cup French’s fried onions
I keep a simple ingredient list so the flavors shine. For more of my recipes, visit my homepage at https://www.dulciarecipes.com/.
Instructions
- Place rack in middle of oven; preheat oven to 375° F.
- Working in batches, cook 2 lb. fresh green beans in a large pot of boiling salted water until bright green and halfway to tenderness, about 3 minutes per batch. Drain and let cool; trim stem ends.
- Heat 1 Tbsp. extra-virgin olive oil in a large skillet over medium-high. Cook ½ lb. crimini mushrooms, sliced, without stirring, until golden brown underneath, about 2 minutes. Toss and continue to cook, tossing occasionally, until browned on both sides, about 3 minutes more.
- Add 2 Tbsp. unsalted butter and 2 large thyme sprigs to pan. Cook, tossing occasionally, until butter browns and mushrooms are dark brown and very tender, about 4 minutes longer. Season with kosher salt and transfer to a plate.
- Repeat with 2 Tbsp. unsalted butter, salt, and remaining 1 Tbsp. extra-virgin olive oil, ½ lb. crimini mushrooms, sliced, and 2 large thyme sprigs.
- Melt remaining 2 Tbsp. unsalted butter in a large saucepan over medium-low. Whisk in 2 Tbsp. all-purpose flour and cook, whisking occasionally, until roux is golden brown and smells mildly nutty, about 4 minutes.
- Whisk in 1¼ cups whole milk and 1 cup heavy cream. Increase heat and bring to a simmer, whisking often, and cook until béchamel sauce is thick and bubbling, about 5 minutes. Remove from heat and whisk in 4 garlic cloves, finely grated, and ½ cup grated Parmesan; season with salt and freshly ground pepper.
- Arrange green beans and mushrooms in a 2-qt. baking dish. Pour sauce over bean mixture (it may not look like enough, but it will get saucier as it bakes). Cover tightly with foil and bake until sauce is bubbling, 25-30 minutes. Uncover and continue to bake until casserole is lightly browned on top and around the edges, 15-20 minutes longer.
- Top with ¾ cup French’s fried onions and continue to bake just until onions are slightly darker and fragrant, about 3 minutes. Let sit 10 minutes to set before serving.
Green Bean Mushroom Bake Casserole
- Total Time: 1 hr 30 mins
- Yield: 6 servings 1x
Description
A creamy baked casserole of blanched green beans and browned crimini mushrooms in a Parmesan béchamel, topped with crispy fried onions.
Ingredients
- 2 lb. fresh green beans
- Kosher salt
- 2 Tbsp. extra-virgin olive oil, divided
- 1 lb. crimini mushrooms, sliced, divided
- 6 Tbsp. unsalted butter, divided
- 4 large sprigs thyme, divided
- 2 Tbsp. all-purpose flour
- 1? cups whole milk
- 1 cup heavy cream
- 4 garlic cloves, finely grated
- ? cup grated Parmesan
- Freshly ground black pepper
- ? cup French?s fried onions
Instructions
- Place rack in middle of oven; preheat oven to 375?F (190?C).
- Working in batches, cook the green beans in a large pot of boiling salted water until bright green and halfway to tenderness, about 3 minutes per batch; drain, let cool, and trim stem ends.
- Heat 1 Tbsp. extra-virgin olive oil in a large skillet over medium-high heat; cook ? lb. sliced crimini mushrooms without stirring until golden brown underneath, about 2 minutes, then toss and continue to cook, tossing occasionally, until browned on both sides, about 3 minutes more.
- Add 2 Tbsp. unsalted butter and 2 large thyme sprigs to the pan; cook, tossing occasionally, until the butter browns and mushrooms are dark brown and very tender, about 4 minutes longer; season with kosher salt and transfer to a plate.
- Repeat the mushroom browning with the remaining 2 Tbsp. unsalted butter, remaining 1 Tbsp. extra-virgin olive oil, remaining ? lb. sliced crimini mushrooms, 2 large thyme sprigs, and salt.
- Melt the remaining 2 Tbsp. unsalted butter in a large saucepan over medium-low heat; whisk in 2 Tbsp. all-purpose flour and cook, whisking occasionally, until the roux is golden brown and smells mildly nutty, about 4 minutes.
- Whisk in 1? cups whole milk and 1 cup heavy cream; increase heat and bring to a simmer, whisking often, and cook until the b?chamel is thick and bubbling, about 5 minutes; remove from heat and whisk in 4 finely grated garlic cloves and ? cup grated Parmesan; season with salt and freshly ground black pepper.
- Arrange the green beans and mushrooms in a 2-qt. baking dish and pour the sauce over the mixture; cover tightly with foil and bake until the sauce is bubbling, 25?30 minutes, then uncover and continue to bake until the casserole is lightly browned on top and around the edges, 15?20 minutes longer.
- Top with ? cup French?s fried onions and continue to bake just until the onions are slightly darker and fragrant, about 3 minutes; let sit 10 minutes to set before serving.
- Prep Time: 25 mins
- Cook Time: 1 hr 5 mins
Tips
- Brown mushrooms in batches, do not crowd the pan. You want color, not steam.
- Grate garlic finely into the hot sauce after you remove it from heat, this keeps the garlic bright and not bitter.
- If the sauce seems thin before baking, trust it. It thickens as it bakes and the beans release steam.
- To make ahead, assemble and refrigerate covered for up to 24 hours. Add 10-15 minutes to baking time if cold from fridge.
Variations
- Make it vegetarian by using vegetable stock instead of cream for a lighter sauce, or omit Parmesan for a fully vegetarian option.
- Add toasted almonds or panko under the fried onions for extra crunch.
- Swap thyme for rosemary or sage, use sparingly for a different herbal profile.
FAQ
Q: Can I use frozen green beans?
A: Yes. Thaw and pat dry, then reduce blanching time accordingly. You may need to drain excess liquid before baking.
Q: How long will leftovers keep?
A: Store in an airtight container, refrigerated, for up to 3 days. Reheat covered in a 350° F oven until warmed through.
Q: Can I make this dairy free?
A: You can try a dairy-free milk and butter substitute, but the texture and flavor will differ from the original. Parmesan contributes savory umami, so consider a dairy-free umami boost like nutritional yeast.
Conclusion
I hope this green bean mushroom bake becomes a holiday favorite for you. The creamy béchamel and deeply browned mushrooms make this a step above traditional casseroles. If you try it, please leave a comment and let me know how it turned out. For more recipes and baking tips, visit my site at https://www.dulciarecipes.com/.
External resources: my historical reference on the dish is here – https://en.wikipedia.org/wiki/Green_bean_casserole, and food safety guidance is available from the USDA at https://www.usda.gov.