Onion Potato Gratin

Indulge in the ultimate comfort food with this creamy and decadent Onion Potato Gratin. This recipe layers tender Russet potatoes, sweet caramelized onions, and a velvety cheese sauce made from Gruyère and Parmesan, seasoned with aromatic fresh thyme. A hint of cream and a golden, bubbly top make every bite irresistibly rich and satisfying. Perfect as a crowd-pleasing side dish or a standout addition to holiday dinners, this gratin is both hearty and elegant. With its crispy, cheesy crust and melt-in-your-mouth texture, this dish strikes the ideal balance of flavor and texture. Whether you're hosting or simply treating yourself, this Onion Potato Gratin is destined to become a family favorite.

Nutriscore Rating: 63/100

Prep Time:20 mins

Cook Time:75 mins

Total Time:95 mins

Servings: 6

Ingredients

• 5 medium Russet potatoes
• 2 large Yellow onion
• 4 tablespoons Unsalted butter
• 3 tablespoons All-purpose flour
• 2 cups Whole milk
• 1 cup Heavy cream
• 1.5 cups Gruyère cheese, shredded
• 0.5 cups Parmesan cheese, grated
• 1 teaspoon Fresh thyme leaves
• 1 teaspoon Salt
• 0.5 teaspoon Black pepper
• 1 tablespoon Olive oil

Directions

Step 1

Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish lightly with butter or non-stick spray.

Step 2

Peel the potatoes, then slice them evenly into thin rounds, about 1/8-inch thick. Set the slices aside in a bowl of cold water to prevent browning.

Step 3

Halve and thinly slice the onions. Heat olive oil and 1 tablespoon of butter in a large skillet over medium heat. Add the onions, a pinch of salt, and cook, stirring occasionally, until the onions are caramelized (around 20 minutes). Remove from heat and set aside.

Step 4

In a medium saucepan, melt the remaining 3 tablespoons of butter over medium heat. Whisk in the flour and cook for 1-2 minutes, stirring constantly to form a roux.

Step 5

Gradually pour in the milk and heavy cream while whisking to avoid lumps. Cook for 3-5 minutes, or until the mixture thickens slightly. Stir in 1 cup of Gruyère cheese, Parmesan cheese, thyme leaves, salt, and black pepper until the cheese is fully melted. Remove the saucepan from heat.

Step 6

Drain and pat the potato slices dry with a clean kitchen towel. Layer one-third of the potato slices evenly in the prepared baking dish. Spread one-third of the caramelized onions over the potatoes, then pour one-third of the cheese sauce over the top, spreading it evenly. Repeat these layers two more times, finishing with the cheese sauce on top.

Step 7

Sprinkle the remaining 0.5 cup of Gruyère cheese evenly on top of the gratin.

Step 8

Cover the dish with aluminum foil and bake in the preheated oven for 40 minutes. Then, remove the foil and bake uncovered for an additional 30-35 minutes, or until the potatoes are tender and the top is golden and bubbly.

Step 9

Let the gratin rest for 10 minutes before serving. Garnish with extra thyme leaves, if desired.

Nutrition Facts

Serving size	2201.2 grams (2201.2g)

Amount per serving	% Daily Value*
Calories	3497

Total Fat 224.10g	287%
Saturated Fat 125.40g	627%
Polyunsaturated Fat 1.90g
Cholesterol 643mg	214%
Sodium 4645mg	202%
Total Carbohydrate 259.60g	94%
Dietary Fiber 21.10g	75%
Total Sugars 46.30g
Protein 111.10g	222%

Vitamin D 251IU	1254%
Calcium 2875mg	221%
Iron 13mg	70%
Potassium 6189mg	132%

*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: 57.6%

Protein: 12.7%

Carbs: 29.7%