This onion casserole is made with sautéed caramelized onions tossed in a creamy, cheesy sauce with buttery crackers on top. Every bite is outrageously flavorful, and this makes the perfect side for any occasion!
This onion casserole recipe takes plain old onions and turns them into a flavorful casserole that even the picky eaters at the table will love! It's fit for every occasion and will pair well with any meal.
It makes a delicious and easy weeknight side dish served with things like this chicken pot pie with biscuits or the perfect addition to Thanksgiving or any holiday dinner. For what it's worth, it's one of my favorite Thanksgiving casseroles.
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Why You'll Love This Recipe
It's foolproof. This recipe just involves sauteeing the onions, mixing them in the sauce, and assembling the casserole. The oven takes over from there, and the process is effortless!
Everyone always loves it. People are always a little weary when I serve this since onions are the main thing, but after one bite, they're addicted. Even people who don't typically like onions will go for seconds!
The flavor. The combination of caramelized Vidalia onions mixed with the cheesy, creamy sauce and topped with buttery crushed crackers creates an unbeatable flavor you won't find anywhere else.
- Onions- sweet onions, thinly sliced.
- Butter- unsalted butter since we'll be adding some salt.
- Salt and black pepper- for flavor.
- Mayonnaise and sour cream- to create the creamy sauce.
- Parmesan cheese and cheddar cheese- a delicious cheesy combo.
- Ritz crackers- crushed for the crunchy topping.
By the way, if you end up with extra onions, check out this French onion chicken casserole or this Brenda Gantt cabbage casserole recipe. They're two of my favorite casseroles with tons of onion flavor, so definitely give those a try next!
How To Make Onion Casserole
1. Cook the onions: Preheat a large skillet over low heat. Melt butter in the skillet, then add the onions, salt, and pepper. Sauté the onions for 45-60 minutes, stirring every few minutes, until the onions are soft, translucent, and slightly golden. When the onions are soft, transfer them to a large bowl.
2. Prep to bake: Preheat the oven to 350°F (180°C) and lightly grease a 3-4 quart baking dish with cooking spray.
3. Make the casserole filling: Mix the cooked onions with mayo, sour cream, parmesan cheese, and cheddar cheese. Transfer the onion mixture to the prepared baking dish and top with the crushed cracker crumbs.
4. Bake and serve: Transfer the baking dish to the preheated oven and bake uncovered for 30 minutes or until the top is bubbly and golden brown. Serve warm, and enjoy!
- Use softened cream cheese instead of mayonnaise for a thicker, extra decadent casserole sauce.
- Substitute the Ritz cracker crumbs for bread crumbs or Corn Flakes for a different crunchy topping.
- Use other types of cheese, like shredded provolone, swiss, or pepper jack, for a spicy kick.
- Garnish the finished casserole with fresh herbs or green onions for a pop of color.
How To Store and Reheat Leftovers
In the fridge: Store any leftovers in an airtight container in the fridge for up to 5 days.
In the freezer: Allow the leftover casserole to cool completely, then transfer it to a freezer-safe bag or container and freeze for up to 6 months.
Reheating: Put the casserole back in a baking dish and warm in the oven at 350°F for about 10 minutes. If it's frozen, add more reheating time or let it thaw in the fridge overnight.
Frequently Asked Questions
Can I make this ahead of time?
Yes, you can make this recipe ahead of time. Just cook the casserole filling and store it in the baking dish with the lid on, without the cracker crumbs. When you're ready to bake, add the cracker crumbs to the casserole dish, then bake the casserole as normal.
What onions are best for this casserole?
I like to use sweet onions, specifically Vidalias, since the sweet flavor makes this casserole so delicious. With that said, yellow onions or white onions will also work. The casserole will just have a stronger flavor.
What is the difference between a sweet onion and a Vidalia onion?
Vidalia onions are a type of sweet yellow onion. They have a higher sugar content than other types of sweet onions, giving them a sweeter flavor making them great for cooking.
More Casserole Recipes
- Zucchini pizza casserole
- Mixed veggie casserole
- Squash casserole
- Tomato casserole
- Brussel sprout casserole
- Spinach artichoke chicken casserole
- 2 lbs. (900g) sweet onions, thinly sliced
- ½ cup of butter
- 1 teaspoon salt
- ½ tsp. black pepper
- ¼ cup mayonnaise
- ¼ cup sour cream
- ¼ cup grated parmesan cheese
- 1 cup cheddar cheese, grated
- 15 Ritz crackers, crushed
- Heat a large skillet over low heat. Once hot, add the butter, onions, salt, and pepper.
- Sauté the onions for 45-60 minutes, stirring every few minutes, until the onions are soft, translucent, and slightly golden.
- Preheat the oven to 350°F (180°C) and grease a 3-4 qt baking dish with cooking spray.
- Transfer the sauteed onions to a large bowl. Add the mayo, sour cream, parmesan, and cheddar cheese and mix fully with the onions.
- Spoon the onion mixture into the prepared baking dish and top with the crushed crackers.
- Bake for 30 minutes until bubbly and golden on top.
Serving Size:1 cup
Amount Per Serving: Calories: 354Total Fat: 28gSaturated Fat: 0gTrans Fat: 0gUnsaturated Fat: 0gCholesterol: 0mgSodium: 0mgCarbohydrates: 17gFiber: 2gSugar: 0gProtein: 10g