Onion Casserole
Sweet Onion Casserole puts humble onions front and center, with layers of tender sautéed sweet onions, melty Swiss cheese, and buttery cracker crumbs baked until golden. It’s a rich, savory, Southern side that’s easy to make ahead, perfect for a weeknight dinner or a potluck. Vidalia or Texas 1015 onions turn sweet and mellow in the oven. Made with pantry staples, it comes together in about 35 minutes and serves 9.
Did you know there’s an onion so sweet it was once called the sweetest in the world? The 1015 onion, was developed by a Texas A&M professor, and apparently a very big deal if you’re from Texas. I am not, so this was news to me.
But I get it, because I feel the same way about my Vidalias. And science!!
Here in Georgia, the Vidalia is the sweet onion of choice, and honestly, I could eat them raw, they’re that good. So I made them the star of this casserole.
Sautéed sweet onions, layered with tangy Swiss cheese and buttery cracker crumbs, and baked until golden brown and bubbly. The onions turn soft and sweet in the oven, and the cracker topping gets crispy.
It’s a delicious, savory side that surprises people, since nobody expects onions to be the main event.
It’s perfect for a weeknight side or a potluck, and it’s easy to prep ahead. if onions are your thing, I have some more recipes for you to try.
More Vegetable Casseroles
- Squash Casserole – creamy cheesy Southern baked squash
- Cabbage Casserole – buttery baked cabbage comfort dish
- Veg All Casserole – classic mixed vegetable and cheese comfort bake
- Pea Casserole – creamy comforting baked pea casserole
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See recipe card for complete information on ingredients and their quantities.
Ingredient Notes
Sweet Onions – Vidalia onions, Texas 1015 onions, or mild yellow onions are best. They turn sweet and mellow as they cook, which is the whole point. Red onions and Spanish onions are a little too strong for this casserole so I would hold off on using those.
Swiss Cheese – I know it seems like a strange choice, but it adds a tangy, nutty flavor that really works with the sweet onions. Cheddar, mozzarella, or Monterey Jack all work if Swiss isn’t your thing.
Saltine Crackers – I use Saltine crackers because they are easiest and hold up during the baking and stay crunchy on top. Use Ritz, or another buttery cracker. Panko crumbs and cornflakes work in a pinch.
Evaporated Milk – This is combined with eggs to make a light binder that holds the layers together. Heavy cream or half and half sub in fine.
Eggs – Use large eggs, at room temperature, and mix with the milk to help bind the casserole together. They also make the sauce extra rich.
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How To Make Sweet Onion Casserole
- Preheat the oven to 350°F. In a large skillet, sauté the sliced onions in 1/4 cup butter over medium heat until tender.
- Layer half the onions in the bottom of an 8×8 baking dish. Cover with 1 cup of the Swiss cheese and 3/4 cup of the saltine crumbs.
- Add the remaining onions in a layer and top with the remaining cheese. In a bowl, whisk together the eggs, evaporated milk, salt, and pepper. Pour over the onion layers.
- Melt the 3 tablespoons butter and mix it with the remaining cracker crumbs. Spread over the top. Bake at 350°F for 20 to 25 minutes, until bubbly and the topping is golden brown.
For the full recipe and detailed instructions, please refer to the recipe card at the bottom of the post.
Storage & Reheating
Refrigerator: Store in an airtight container for up to 3 days. Reheat in the microwave or a 350°F oven until heated through. If it seems dry, add a little chicken broth.
Make Ahead: Sauté the onions and store them covered in the fridge up to 3 days. Make the cracker topping ahead and keep it in a bag, then assemble and bake when ready.
Topping Tip: Add the buttered cracker topping right before baking so it crisps up when it bakes instead of getting soggy.
Freezer: Onions don’t hold up that well when frozen, at least when you freeze them at home. This is best made fresh. You can always prep a few days ahead of time if you need to free up some time and stress.
Variations
Different Cheese: Swap the Swiss cheese for cheddar, mozzarella, or Monterey Jack. Add Pepper Jack for a little kick.
Different Topping: Use Ritz, panko, cornflakes, or crushed potato chips for maximum crunch.
Cheesier Top: Mix Parmesan or sharp cheddar with a tablespoon of butter into the topping.
Richer Flavor: Add a pinch of brown sugar and a dash of soy sauce to deepen the flavor.
Extra Crunch: Crush potato chips over the top for a salty, crispy finish.
More Onion Recipes
- French Onion Chicken Casserole – caramelized onion with biscuit topping
- Air Fryer Blooming Onion – crispy pull apart onion with no deep frying
- French Onion Dip – rich caramelized onion dip for chips and veggies
- French Onion Meatballs – savory saucy party ready meatballs
Frequently Asked Questions
Sweet onions like Vidalia, 1015, or mild yellow onions are best. They turn soft, sweet, and mellow as they bake, which is the whole idea of the recipe.
Yes. Sauté the onions and refrigerate them up to 3 days, and make the cracker topping ahead. Assemble and bake when you’re ready, adding the topping right before baking.
Cheddar, mozzarella, and Monterey Jack all work well and melt smooth if you’d rather not use Swiss.
Chill or freeze the onions for 30 minutes before slicing, and set a damp paper towel nearby to absorb the fumes. Both tricks cut down on the tears. I have tried the whole “bread in the mouth” trick but it didn’t work for me.
It’s a nice vegetarian side, great with rotisserie chicken, burgers, or a baked potato. It’s hearty enough to be the star of a Meatless Monday too.
Up to 3 days in an airtight container in the fridge. Add a splash of chicken broth when reheating if it seems dry. You can even add a little more of the cracker topping if you like.
Recipe Tips & Tricks
- Cut the onions in half before slicing to make it easier, or leave them in rings if you prefer.
- Chill or freeze the onions for 30 minutes before cutting to avoid tears.
- Add the buttered cracker topping right before baking so it stays crisp.
- Spray the dish well so the casserole doesn’t stick.
- Add a pinch of brown sugar and a dash of soy sauce for a richer, deeper flavor.
This Sweet Onion Casserole recipe is rich, savory, and turns humble onions into the star of the table. Make it for your next potluck or weeknight side and watch everyone ask what’s in it!
If you love this recipe as much as I do, please leave us a ⭐️⭐️⭐️⭐️⭐️ five-star review in the comment section below. Thanks!
Sweet Onion Casserole
Ingredients
- ¼ cup unsalted butter
- 3 large sweet onions peeled, sliced
- 2 cups Swiss cheese shredded, divided
- 2 large eggs room temperature
- ¼ cup evaporated milk
- 1 teaspoon salt
- ½ teaspoon pepper
- 1 ½ cups saltine crackers crushed, divided
- 3 tablespoons unsalted butter
Instructions
- Preheat oven to 350F.
- In a large skillet, saute the onions in the ¼ cup butter over medium heat until tender.
- Layer ½ the onion mixture in bottom of a 8×8 baking pan.
- Cover with 1 cup Swiss cheese.
- Top with 3/4 cup saltine crumbs.
- Add remaining onions in a layer and top with remaining cheese.
- In a bowl, combine the eggs, milk, and seasonings.
- Pour over onion layers.
- Melt 3 tablespoons butter and mix with remaining cracker crumbs.
- Spread over top of casserole.
- Bake at 350F for 20-25 minutes or until bubbly and the topping is golden brown.
Notes
- Cut the onions in half before slicing to make it easier, or leave them in rings if you prefer.
- Chill or freeze the onions for 30 minutes before cutting to avoid tears.
- Add the buttered cracker topping right before baking so it stays crisp.
- Spray the dish well so the casserole doesn’t stick.
- Add a pinch of brown sugar and a dash of soy sauce for a richer, deeper flavor.
Nutrition
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