Caramelized Onion Potatoes au Gratin Recipe
This Caramelized Onion Potatoes au Gratin recipe combines tender russet potatoes simmered in a fragrant cream mixture with sweet, deeply caramelized onions and melted Gruyere cheese for a rich, comforting side dish perfect for special occasions or cozy dinners.
- Prep Time: 25 minutes
- Cook Time: 55 minutes
- Total Time: 1 hour 20 minutes
- Yield: 8 servings 1x
- Category: Side Dish
- Method: Baking
- Cuisine: French
Ingredients
Scale
Butter and Onions
- 4 tablespoons unsalted butter, divided
- 2 sweet yellow onions, thinly sliced
- 1 teaspoon sugar
Potatoes and Dairy
- 4 lbs large russet potatoes (about 4-7), peeled and sliced about 1/8″ (3mm) thick on a mandoline
- 2 1/2 cups heavy cream
- 1 1/2 cups half & half
- 3 garlic cloves, grated
Herbs and Spices
- 2–3 sprigs fresh thyme
- 2 bay leaves
- Pinch of nutmeg
- Kosher salt, to taste
- Freshly ground black pepper, to taste
Cheese
- 6 oz Gruyere cheese, shredded
Instructions
- Caramelize the Onions: In a medium skillet, melt 2 tablespoons of butter over medium-low heat. Add the thinly sliced onions and toss to coat. Cover the pan for 5 minutes to help the onions wilt. Season with salt and pepper, then cook, stirring occasionally until the onions turn golden brown. Sprinkle with sugar and continue cooking until the onions are deeply amber in color. Set aside and allow to cool.
- Simmer the Potatoes: In a 4-quart pot or Dutch oven, combine the heavy cream, half & half, grated garlic, fresh thyme sprigs, bay leaves, and a pinch of nutmeg. Season with kosher salt and freshly ground pepper. Add the sliced potatoes to the pot and bring to a gentle simmer over low heat. Cook for about 15 minutes, until the potatoes are just starting to become tender. Adjust seasoning with salt and pepper if needed. Remove from heat and let the mixture rest for 10 minutes.
- Prepare the Baking Dish: Preheat the oven to 375°F (190°C). Butter a 3-quart baking dish with the remaining 2 tablespoons of butter. Discard the thyme sprigs and bay leaves from the potato and cream mixture.
- Assemble the Gratin: Using a slotted spoon, transfer half of the potatoes into the prepared baking dish. Layer half of the caramelized onions and half of the shredded Gruyere cheese over the potatoes. Cover with the remaining potatoes. Pour the remaining creamy sauce over the layered potatoes, and top with the remaining onions and cheese.
- Bake Until Golden: Bake the gratin uncovered for 35-40 minutes, until the cheese is bubbly and golden brown and the potatoes are tender when pierced with a knife.
- Rest and Serve: Allow the gratin to rest for 15 minutes before serving to let it set. Optionally, garnish with additional fresh thyme for aroma and presentation.
Notes
- Use a mandoline slicer for uniformly thin potato slices to ensure even cooking.
- Do not skip resting the potatoes after simmering to help the flavors meld.
- Gruyere adds a nutty, creamy flavor, but you can substitute with other melting cheeses like Emmental or Fontina.
- Make sure to peel the potatoes to avoid a tough texture in the gratin.
- For a crispier top, broil for the last 2-3 minutes watching carefully to avoid burning.
- This dish can be prepared a day ahead and reheated in the oven for convenience.
Keywords: potatoes au gratin, caramelized onions, Gruyere cheese, creamy potato casserole, French side dish, comfort food
