Let me tell you about this incredible Southern Sweet Onion Casserole! Imagine layers of thinly sliced sweet onions, mixed with creamy, cheesy sauce, and topped with a buttery cracker crumb crust. The sweetness of the onions perfectly balances the savory richness of the sauce, creating a delectable combination of flavors.

This casserole is comfort food at its finest, with each bite offering a satisfying blend of textures and tastes. Whether served as a side dish or a main course, this dish never fails to impress with its southern charm and irresistible taste. Trust me, one bite of this Southern Sweet Onion Casserole, and you’ll be amazed!

Ingredients Needed for This Recipe

4 tablespoons unsalted butter, plus more for greasing the baking dish
3 large sweet onions, such as Vidalia, thinly sliced
2 cloves garlic, minced

1 teaspoon sugar
1/2 teaspoon salt
1/4 teaspoon black pepper

1/4 teaspoon paprika
2 tablespoons all-purpose flour
1 cup milk

1/2 cup sour cream
1 cup grated sharp cheddar cheese
1/2 cup grated Parmesan cheese

1 cup crushed buttery round crackers (such as Ritz), for topping
2 tablespoons unsalted butter, melted, for topping

Instructions for Making Southern Sweet Onion Casserole

Preheat the oven and prepare the baking dish: Preheat your oven to 350°F (175°C). Grease a medium-sized baking dish with butter.

Cook the onions: In a large skillet over medium heat, melt 4 tablespoons of butter. Add the sliced onions and garlic, and cook, stirring occasionally, until the onions are soft and beginning to caramelize, about 15-20 minutes. Sprinkle the sugar, salt, pepper, and paprika over the onions, and stir to combine.
Make the sauce: Sprinkle the flour over the cooked onions and stir until the onions are well-coated. Gradually add the milk, stirring constantly, until the mixture is smooth and thickens, about 5 minutes. Remove from heat and stir in the sour cream, half of the cheddar cheese, and half of the Parmesan cheese until well combined.
Assemble the casserole: Transfer the onion mixture to the prepared baking dish. Sprinkle the remaining cheddar and Parmesan cheeses over the top. In a small bowl, mix the crushed crackers with the melted butter, then sprinkle this mixture evenly over the cheese.

Bake the casserole: Bake in the preheated oven until the topping is golden brown and the casserole is bubbly, about 25-30 minutes.
Serve: Let the casserole stand for a few minutes before serving. This allows it to set slightly, making it easier to serve.

Tips for Perfecting the Recipe

Choosing the Right Onions: The key to this casserole’s delightful sweetness lies in the type of onions used. Vidalia onions are perfect due to their natural sweetness, but Walla Walla or Texas Sweet onions are excellent substitutes. The sweetness of these onions contrasts beautifully with the savory components of the dish.

Slicing the Onions: Thin, uniform slices of onion are crucial for even cooking and caramelization. Use a sharp knife or a mandoline slicer to achieve consistent thickness. This ensures that all onion pieces become tender and sweet as they cook.

Caramelizing Onions: Patience is vital when caramelizing onions. The process can take upwards of 20 minutes, but it’s worth it for the depth of flavor achieved. Cook them over medium heat and avoid rushing this step; the natural sugars need time to gently brown and develop their sweetness.

Roux and Sauce Consistency: The roux, made from butter and flour, thickens the sauce. It’s essential to cook the roux for a couple of minutes to eliminate the raw flour taste. When adding milk, do so gradually while constantly stirring to prevent lumps. Aim for a creamy consistency that’s not too thick or thin, as it will continue to thicken in the oven.

Cheese Selection: The recipe calls for sharp cheddar and Parmesan, which provide a nice balance of flavor and meltiness. Feel free to experiment with other cheeses, but ensure they offer a good melt and complement the sweet onions. A combination of Gruyère and mozzarella can also work well for a stretchy texture and nutty taste.

Cracker Topping: The buttery cracker topping adds a delightful crunch and rich flavor to the casserole. Crush the crackers finely for a more even texture, and thoroughly mix them with melted butter to ensure they toast nicely in the oven. For a variation, adding a sprinkle of dried herbs like thyme or rosemary to the topping can introduce a lovely aromatic component.

Serving Suggestions

As a Side Dish: This casserole pairs beautifully with a variety of main courses. Serve it alongside grilled or roasted meats, such as beef, pork, or chicken, for a meal that’s sure to impress. It’s also a fantastic complement to Thanksgiving turkey or Christmas ham.

With Vegetarian Mains: The casserole’s rich, savory flavor makes it a great side for vegetarian dishes. Pair it with a quinoa or farro salad, stuffed bell peppers, or a hearty vegetable stew for a satisfying meal.

Potluck or Buffet: Due to its ease of serving and popularity, this casserole is perfect for potlucks or buffet-style gatherings. It can be made ahead of time and reheated, making it convenient for hosts and guests alike.

Brunch Option: For a unique brunch offering, serve the casserole with a side of mixed greens and a light vinaigrette. Its richness pairs well with the freshness of the salad, offering a balanced meal.

Storage Tips

Cooling and Storing: Allow the casserole to cool completely before covering it with plastic wrap or aluminum foil. It can be refrigerated for up to 3-4 days. Ensure the container is airtight to prevent the onions from absorbing any fridge odors.

Freezing: This casserole freezes well, making it a great make-ahead option. Freeze it in an airtight container for up to 2 months. To serve, thaw it overnight in the refrigerator before reheating.

Reheating: To reheat, cover the casserole with foil and warm it in a 350°F oven until heated through, about 20-25 minutes. If the topping lacks crispness, remove the foil for the last few minutes of heating.

Frequently Asked Questions

Can I make this casserole ahead of time? Yes, you can assemble the casserole, cover, and refrigerate it a day in advance. Add an extra 5-10 minutes to the baking time if it goes into the oven cold from the fridge.

Can I use low-fat ingredients? While full-fat dairy products offer the best flavor and texture, low-fat milk and sour cream can be used for a lighter version. However, the overall creaminess may be slightly reduced.

What can I do if my onions aren’t caramelizing? Onions may not caramelize properly if the heat is too high or too low. Ensure the heat is set to medium and give them time. If they start to dry out, you can add a tablespoon of water to help release the sugars.

Can I add other vegetables to this casserole? Yes, adding other vegetables can introduce new flavors and textures. Consider mushrooms, bell peppers, or spinach. Just make sure to cook any additional vegetables before adding them to the casserole to ensure they’re tender and to prevent excess moisture.

Is there a gluten-free option? For a gluten-free version, substitute the all-purpose flour with a gluten-free flour blend for the roux, and use gluten-free crackers for the topping.

Southern Sweet Onion Casserole

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Southern Sweet Onion Casserole is a comforting and flavorful dish that highlights the natural sweetness of onions, enhanced by a creamy sauce and a crunchy topping.

Ingredients

4 tablespoons unsalted butter plus more for greasing the baking dish
3 large sweet onions such as Vidalia, thinly sliced

2 cloves garlic minced
1 teaspoon sugar
1/2 teaspoon salt

1/4 teaspoon black pepper
1/4 teaspoon paprika
2 tablespoons all-purpose flour

1 cup milk
1/2 cup sour cream
1 cup grated sharp cheddar cheese

1/2 cup grated Parmesan cheese
1 cup crushed buttery round crackers such as Ritz, for topping
2 tablespoons unsalted butter melted, for topping

Instructions

Preheat the oven and prepare the baking dish: Preheat your oven to 350°F (175°C). Grease a medium-sized baking dish with butter.
Cook the onions: In a large skillet over medium heat, melt 4 tablespoons of butter. Add the sliced onions and garlic, and cook, stirring occasionally, until the onions are soft and beginning to caramelize, about 15-20 minutes. Sprinkle the sugar, salt, pepper, and paprika over the onions, and stir to combine.
Make the sauce: Sprinkle the flour over the cooked onions and stir until the onions are well-coated. Gradually add the milk, stirring constantly, until the mixture is smooth and thickens, about 5 minutes. Remove from heat and stir in the sour cream, half of the cheddar cheese, and half of the Parmesan cheese until well combined.

Assemble the casserole: Transfer the onion mixture to the prepared baking dish. Sprinkle the remaining cheddar and Parmesan cheeses over the top. In a small bowl, mix the crushed crackers with the melted butter, then sprinkle this mixture evenly over the cheese.
Bake the casserole: Bake in the preheated oven until the topping is golden brown and the casserole is bubbly, about 25-30 minutes.
Serve: Let the casserole stand for a few minutes before serving. This allows it to set slightly, making it easier to serve.