Heavenly Onion Casserole

Indulge in the rich, savory decadence of Heavenly Onion Casserole, a comfort food masterpiece that brings caramelized onions to center stage. This easy-to-make dish combines velvety cream sauce infused with thyme and garlic with layers of Gruyere and Parmesan cheeses, creating a luxurious flavor profile that’s sure to impress. Finished with a golden, crispy panko breadcrumb topping, this casserole balances creamy richness with irresistible crunch in every bite. Perfect as a side dish for holidays or a crowd-pleasing centerpiece for weeknight dinners, this casserole is a must-try for onion lovers. Ready in just over an hour and serving up to six, it’s simple, satisfying, and utterly heavenly!

Nutriscore Rating: 58/100

Prep Time:25 mins

Cook Time:40 mins

Total Time:65 mins

Servings: 6

Ingredients

• 5 large yellow onions
• 4 tablespoons butter
• 3 tablespoons all-purpose flour
• 2 cups whole milk
• 1 cup heavy cream
• 1 cup grated Parmesan cheese
• 1.5 cups shredded Gruyere cheese
• 1 cup panko breadcrumbs
• 1 tablespoon olive oil
• 1 teaspoon salt
• 1 teaspoon black pepper
• 1 teaspoon fresh thyme leaves
• 0.5 teaspoon garlic powder

Directions

Step 1

Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch casserole dish and set it aside.

Step 2

Peel and slice the onions into thin rings or half-moons. Aim for even slices for consistent cooking.

Step 3

In a large skillet, melt 2 tablespoons of butter over medium heat. Add the onions, salt, and pepper. Cook, stirring occasionally, for 15–20 minutes until the onions are soft and caramelized. Remove from heat.

Step 4

In a medium saucepan, melt the remaining 2 tablespoons of butter over medium heat. Whisk in the flour and cook for 1 minute to remove the raw taste of the flour.

Step 5

Gradually whisk in the milk and heavy cream, ensuring no lumps form. Continue whisking until the sauce thickens, about 3–4 minutes. Stir in the garlic powder, thyme, and half of the Parmesan cheese.

Step 6

Transfer the caramelized onions to the prepared casserole dish and pour the cream sauce evenly over the top.

Step 7

Sprinkle the Gruyere cheese evenly over the onions, followed by the remaining Parmesan cheese.

Step 8

In a small bowl, combine the panko breadcrumbs and olive oil. Mix well until the breadcrumbs are evenly coated. Sprinkle the breadcrumb mixture over the top of the cheese layer.

Step 9

Place the casserole in the preheated oven and bake for 25–30 minutes, or until the top is golden brown and bubbling.

Step 10

Remove from the oven and let the casserole rest for 5–10 minutes before serving. Enjoy the rich and cheesy flavors of this savory onion casserole!

Nutrition Facts

Serving size	1878.8 grams (1878.8g)

Amount per serving	% Daily Value*
Calories	3210

Total Fat 236.40g	303%
Saturated Fat 131.10g	656%
Polyunsaturated Fat 3.30g
Cholesterol 690mg	230%
Sodium 5848mg	254%
Total Carbohydrate 153.30g	56%
Dietary Fiber 16.10g	58%
Total Sugars 60.10g
Protein 114.60g	229%

Vitamin D 260IU	1299%
Calcium 3305mg	254%
Iron 7mg	37%
Potassium 2031mg	43%

*The % Daily Value tells you how much a nutrient in a serving of food contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.

Source of Calories

Fat: 66.5%

Protein: 14.3%

Carbs: 19.2%