Caramelized Onion Green Bean Casserole with fresh green beans in a creamy sauce topped with sweet onions and buttery breadcrumbs. Serve with Roasted Vegetable Wellington and Chipotle Mashed Sweet Potatoes.

No Mushroom Green Bean Casserole
I like this green bean casserole because it’s made with fresh ingredients. The flavor is rich, savory with a touch of sweet; perfect for Christmas or Thanksgiving dinner and throughout the holiday season. It also has all the comfort of a classic green bean casserole, with none of the cream of mushroom soup or other canned shortcuts.

Ingredients for Caramelized Onion Green Bean Casserole
Here’s what you’ll need. Exact amounts are listed in the printable recipe card at the bottom of the post.
- Yellow Onions – Thinly sliced and cooked slowly in butter until sweet and golden.
- Butter – Used with the onions, the sauce, and the topping for richness all the way through.
- Simple Seasonings – Kosher salt and ground black pepper for balance.
- Sherry Wine – A splash to deglaze the pan adds depth and sweetness to the onions. White wine or vegetable broth can be used as an alternative.
- All-Purpose Flour – Helps the sauce thicken so it coats the beans instead of pooling at the bottom.
- Half-and-Half – The base of the creamy white sauce.
- Nutmeg, Cayenne, and Thyme – A little of each brings depth and warmth to the sauce.
- Panko Breadcrumbs – Toasted in butter until golden for a crunchy finish on top. Regular breadcrumbs do not bring the same texture and are not recommended for this recipe.
- Parmesan and Gruyere Cheeses – Gruyere melts into the sauce and on top, while Parmesan is mixed into the breadcrumb topping for extra flavor. Together they make the casserole rich, creamy, and savory.
- Fresh Green Beans – Blanched just until tender-crisp, then baked in the sauce. Snapping or cutting them into halves or thirds makes them easier to eat in casserole form.
Can I Use Canned or Frozen Green Beans?
Canned green beans aren’t recommended for this recipe. They’re already very soft, and by the time the casserole is baked, they turn mushy. Frozen green beans can work if you don’t have fresh, but they need to be thawed and drained well to avoid excess water in the sauce. Fresh green beans give the best texture and hold up well through blanching and baking.
How to Make Caramelized Onion Green Bean Casserole
STEP ONE: Prep. Preheat oven to 375°F. Grease an 8×8-inch baking dish with non-stick cooking spray.
STEP TWO: Caramelize Onions. Set a large skillet over medium heat and add butter. When melted, add onions, salt, and pepper. Cook for 10 minutes, stirring often, until soft and lightly caramelized. Stir in the sherry and cook 1 minute more. Transfer onions to a bowl and set aside.
STEP THREE: Blanch the Green Beans. Bring a large pot of salted water to a boil. Add green beans and cook for 3 minutes, until bright green and just crisp-tender. Drain well and set aside.
STEP FOUR: Make White Sauce. Return the skillet to medium heat and melt butter. Whisk in the flour and cook 1 minute. Slowly whisk in half-and-half. Add nutmeg, cayenne, and thyme. Lower heat and simmer, whisking frequently, until slightly thickened. Remove from heat and stir in half the Gruyere until melted.
STEP FIVE: Combine. Add the cooked green beans to the skillet and stir gently to coat.
STEP SIX: Prepare the Topping. In a medium bowl, combine breadcrumbs, Parmesan, and melted butter.
STEP SEVEN: Assemble. Transfer the green bean mixture to the prepared baking dish. Sprinkle with the remaining Gruyère. Top with caramelized onions and the breadcrumb mixture.
STEP EIGHT: Bake. Bake for 20 minutes. Loosely cover with foil and continue baking 10 minutes, until heated through.
STEP NINE: Serve. Let the casserole sit for 10 minutes to set. Serve warm.

Can I Double this Recipe?
Yes. Assemble it in a 9×13-inch baking dish instead of an 8×8. Since there’s more volume, the casserole will need a little extra time in the oven to heat evenly all the way through. Add about 10 minutes to the baking time and check that it’s hot in the center before serving.
Make it Vegan 🌱
For a plant-based casserole, use dairy-free butter, half-and-half (oat-based half-and-half works best; coconut-based gives the wrong flavor), and Parmesan cheese. Vegan Gruyère cheese is difficult to find outside of specialty shops, but dairy-free Swiss is a good alternative.

Storage and Reheating
- Store leftovers in an airtight container in the refrigerator. Reheat in a 350°F oven or in the microwave.
More Recipes You’ll Love
- Green Bean Rice
- Slow Cooker Green Bean Casserole
- No Mushrooms Green Bean Casserole
- Green Bean and Potato Casserole
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Caramelized Onion Green Bean Casserole Recipe
Ingredients
For the Onions
- 3 tablespoons butter
- 2 ½ cups yellow onions thinly sliced
- 1/2 teaspoon kosher salt
- 1/2 teaspoon ground black pepper
- 1 tablespoon sherry wine
For the Green Beans
- 1 ½ pounds fresh green beans trimmed
For the White Sauce
- 2 tablespoons butter
- 2 tablespoons all-purpose flour
- 1 2/3 cups half-and-half
- 1/4 teaspoon kosher salt
- 1/8 teaspoon ground nutmeg
- 1/8 teaspoon cayenne pepper
- 1/8 teaspoon dried thyme leaves
- 1 cup Gruyere cheese divided
For the Topping
- 1/2 cup panko bread crumbs
- 3 tablespoons Parmesan cheese grated
- 2 tablespoons butter melted
Instructions
- Preheat oven to 375°F. Grease an 8×8-inch baking dish with non-stick cooking spray.
- Set a large skillet over medium heat and add butter. When melted, add onions, salt, and pepper. Cook for 10 minutes, stirring often, until soft and lightly caramelized. Stir in the sherry and cook 1 minute more. Transfer onions to a bowl and set aside.
- Bring a large pot of salted water to a boil. Add green beans and cook for 3 minutes, until bright green and just crisp-tender. Drain well and set aside.
- Return the skillet to medium heat and melt butter. Whisk in the flour and cook 1 minute. Slowly whisk in half-and-half. Add nutmeg, cayenne, and thyme. Lower heat and simmer, whisking frequently, until slightly thickened. Remove from heat and stir in half the Gruyere until melted.
- Add the cooked green beans to the skillet and stir gently to coat.
- In a medium bowl, combine breadcrumbs, Parmesan, and melted butter.
- Transfer the green bean mixture to the prepared baking dish. Sprinkle with the remaining Gruyère. Top with caramelized onions and the breadcrumb mixture.
- Bake for 20 minutes. Loosely cover with foil and continue baking 10 minutes, until heated through.
- Let the casserole rest for 10 minutes to set. Serve warm.
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