Onion Sandwich Au Gratin

Indulge in the savory decadence of Onion Sandwich Au Gratin, a comforting baked dish that transforms humble ingredients into a gourmet masterpiece. Layers of golden, caramelized yellow onions are nestled between toasted slices of rustic bread and smothered with creamy Dijon-infused sauce. Topped with nutty Gruyere cheese and a crisp panko-Parmesan breadcrumb crust, this casserole-style take on the classic sandwich offers a rich, cheesy bite with every forkful. Perfect for dinners or an impressive brunch centerpiece, this recipe is simple yet elegant, with only 20 minutes of prep time. Finished with a sprinkle of fresh parsley, this crowd-pleaser guarantees a golden, bubbling delight straight out of your oven.

Nutriscore Rating: 56/100

Prep Time:20 mins

Cook Time:35 mins

Total Time:55 mins

Servings: 4

Ingredients

• 4 medium Yellow onions
• 3 tablespoons Unsalted butter
• 1 tablespoon Olive oil
• 1 teaspoon Salt
• 0.5 teaspoon Black pepper
• 1 teaspoon Granulated sugar
• 8 slices Rustic bread slices
• 2 cups Gruyere cheese
• 0.5 cup Heavy cream
• 1 tablespoon Dijon mustard
• 1 minced Garlic clove
• 0.5 cup Panko breadcrumbs
• 2 tablespoons Fresh parsley
• 0.25 cup Parmesan cheese

Directions

Step 1

Preheat your oven to 400°F (200°C) and grease a large baking dish with butter or cooking spray.

Step 2

Peel and thinly slice the yellow onions.

Step 3

Heat 2 tablespoons of butter and the olive oil in a large skillet over medium heat. Add the onions, salt, and pepper, and cook, stirring occasionally, for about 15 minutes until they soften.

Step 4

Add granulated sugar to the onions and continue cooking for another 5-7 minutes until they are golden brown and caramelized. Remove from heat and set aside.

Step 5

Toast the bread slices lightly under a broiler or in a toaster oven until just crisp. Set them aside on a wire rack to cool.

Step 6

In a small saucepan, heat the heavy cream over low heat. Stir in Dijon mustard and the minced garlic. Allow it to warm through for about 2-3 minutes and set aside.

Step 7

Grate the Gruyere cheese and set aside 1/2 cup for the topping.

Step 8

To assemble the sandwiches, layer half the bread slices in the prepared baking dish. Top each slice with a generous amount of caramelized onions and sprinkle 1.5 cups of the Gruyere cheese over them.

Step 9

Place the remaining bread slices on top to form sandwiches. Spoon the warmed cream mixture evenly over the sandwiches, ensuring it soaks through the bread.

Step 10

Sprinkle the reserved Gruyere cheese over the top of the sandwiches.

Step 11

In a small bowl, combine the panko breadcrumbs, chopped parsley, Parmesan cheese, and the remaining tablespoon of melted butter. Mix well and sprinkle evenly over the top of the dish.

Step 12

Bake in the preheated oven for 15-20 minutes, or until the top is golden brown and bubbly.

Step 13

Allow the dish to cool slightly before serving. Garnish with additional parsley, if desired.

Nutrition Facts

Serving size	1402.4 grams (1402.4g)

Amount per serving	% Daily Value*
Calories	3478

Total Fat 195.80g	251%
Saturated Fat 101.90g	510%
Polyunsaturated Fat 1.30g
Cholesterol 505mg	168%
Sodium 6240mg	271%
Total Carbohydrate 293.40g	107%
Dietary Fiber 17.10g	61%
Total Sugars 32.90g
Protein 131.20g	262%

Vitamin D 0IU	0%
Calcium 3010mg	232%
Iron 15mg	82%
Potassium 1143mg	24%

*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: 50.9%

Protein: 15.2%

Carbs: 33.9%