Oniony Potatoes Au Gratin

Indulge in the creamy, cheesy perfection of Oniony Potatoes Au Gratin, a comforting casserole that elevates classic scalloped potatoes with the rich, savory sweetness of caramelized onions. Thinly sliced russet potatoes are layered with golden onions, a velvety cheese sauce made with Gruyère and sharp cheddar, and a fragrant hint of fresh thyme. The dish is finished with an option for a golden breadcrumb topping, adding a delightful crunch. Perfect for holidays, family dinners, or any special occasion, this easy-to-follow recipe combines simple ingredients with elevated flavors for a side dish that steals the spotlight. Serve warm and bask in the irresistible aroma of baked goodness straight from the oven!

Nutriscore Rating: 65/100

Prep Time:30 mins

Cook Time:90 mins

Total Time:120 mins

Servings: 6

Ingredients

• 4 large Russet potatoes
• 2 medium Yellow onion
• 6 tablespoons Unsalted butter
• 3 tablespoons All-purpose flour
• 2.5 cups Whole milk
• 0.5 cups Heavy cream
• 1.5 cups Shredded Gruyère cheese
• 1 cup Shredded sharp cheddar cheese
• 1.5 teaspoons Salt
• 0.5 teaspoons Ground black pepper
• 0.5 teaspoons Fresh thyme leaves
• 1 clove Garlic
• 1 tablespoon Olive oil
• 0.5 cup Breadcrumbs (optional)

Directions

Step 1

Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish with butter or nonstick spray.

Step 2

Peel the potatoes and slice them into 1/8-inch thick rounds using a mandolin or a sharp knife. Set aside in a bowl of cold water to prevent them from browning.

Step 3

Peel and thinly slice the onions. Mince the garlic clove.

Step 4

Heat 1 tablespoon of olive oil and 2 tablespoons of butter in a large skillet over medium heat. Add the onions and a pinch of salt, and cook, stirring occasionally, for 15-20 minutes until the onions are soft and golden brown. Stir in the minced garlic during the last minute of cooking. Remove from heat and set aside.

Step 5

In a medium saucepan, melt the remaining 4 tablespoons of butter over medium heat. Whisk in the flour and cook for 1-2 minutes to form a roux, stirring constantly.

Step 6

Gradually whisk in the milk and heavy cream, ensuring there are no lumps. Cook for 5-7 minutes, stirring frequently, until the mixture thickens slightly.

Step 7

Remove the saucepan from heat and stir in the Gruyère cheese, sharp cheddar cheese, 1 teaspoon of salt, black pepper, and fresh thyme leaves. Mix until the cheese is fully melted and incorporated.

Step 8

Drain the sliced potatoes and pat them dry with a clean kitchen towel.

Step 9

Layer one-third of the sliced potatoes evenly in the bottom of the prepared baking dish. Spread one-third of the caramelized onions over the potatoes. Pour one-third of the cheese sauce over the onions. Repeat this layering process two more times, ending with the cheese sauce on top.

Step 10

If using breadcrumbs, sprinkle them evenly over the top layer of cheese sauce.

Step 11

Cover the dish with aluminum foil and bake in the preheated oven for 50 minutes.

Step 12

Remove the foil and continue to bake for an additional 30-40 minutes, or until the top is golden brown and the potatoes are tender when pierced with a fork.

Step 13

Allow the dish to rest for 10 minutes before serving. Sprinkle additional fresh thyme leaves as a garnish, if desired. Enjoy!

Nutrition Facts

Serving size	2444.9 grams (2444.9g)

Amount per serving	% Daily Value*
Calories	3557

Total Fat 196.30g	252%
Saturated Fat 115.80g	579%
Polyunsaturated Fat 2.00g
Cholesterol 560mg	187%
Sodium 5887mg	256%
Total Carbohydrate 335.50g	122%
Dietary Fiber 25.60g	91%
Total Sugars 52.70g
Protein 136.50g	273%

Vitamin D 304IU	1522%
Calcium 3317mg	255%
Iron 16mg	91%
Potassium 8148mg	173%

*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: 48.3%

Protein: 14.9%

Carbs: 36.7%