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.
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Recipe Information
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
Instructions
Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish lightly with butter or non-stick spray.
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.
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.
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.
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.
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.
Sprinkle the remaining 0.5 cup of Gruyère cheese evenly on top of the gratin.
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.
Let the gratin rest for 10 minutes before serving. Garnish with extra thyme leaves, if desired.
Nutrition Facts
Calories |
589 | ||
|---|---|---|---|
% Daily Value* |
|||
| Total Fat | 37.0 g | 47% | |
| Saturated Fat | 21.6 g | 108% | |
| Polyunsaturated Fat | 0.0 g | ||
| Cholesterol | 105 mg | 35% | |
| Sodium | 699 mg | 30% | |
| Total Carbohydrate | 42.5 g | 15% | |
| Dietary Fiber | 2.9 g | 10% | |
| Total Sugars | 7.7 g | ||
| Protein | 18.3 g | 37% | |
| Vitamin D | 1.3 mcg | 7% | |
| Calcium | 450 mg | 35% | |
| Iron | 1.5 mg | 8% | |
| Potassium | 956 mg | 20% | |
*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.
