Description
These Caramelized Onion Potatoes au Gratin are the ultimate creamy, cheesy comfort food! Thinly sliced russet potatoes are layered with sweet caramelized onions, rich garlic-infused cream, fresh thyme, and nutty Gruyère cheese, then baked until golden and bubbly. Perfect for Thanksgiving, Christmas, holiday gatherings, or a cozy family dinner!
Ingredients
Scale
- 4 tablespoons unsalted butter, divided
- 2 sweet yellow onions, thinly sliced
- 1 teaspoon sugar
- 4 lbs russet potatoes (about 4–7 large potatoes), peeled and sliced ⅛-inch (3 mm) thick
- 2½ cups heavy cream
- 1½ cups half-and-half
- 3 garlic cloves, grated
- 2–3 sprigs fresh thyme
- 2 bay leaves
- 1 pinch ground nutmeg
- 6 oz Gruyère cheese, freshly shredded
- Kosher salt, to taste
- Freshly ground black pepper, to taste
- Fresh thyme, for garnish (optional)
Instructions
- Caramelize the Onions: Melt 2 tablespoons of butter in a medium skillet over medium-low heat. Add the sliced onions, stir to coat, and cover for 5 minutes. Season with salt and pepper, then continue cooking, stirring occasionally, until golden. Sprinkle with sugar and cook until deeply caramelized, about 25–40 minutes total. Set aside.
- Prepare the Cream Sauce: In a 4-quart Dutch oven or large pot, combine heavy cream, half-and-half, grated garlic, thyme sprigs, bay leaves, nutmeg, salt, and black pepper. Stir gently.
- Simmer the Potatoes: Add the thinly sliced potatoes to the cream mixture. Bring to a gentle simmer over low heat and cook for approximately 15 minutes, until the potatoes begin to soften. Stir carefully to prevent sticking. Adjust seasoning as needed.
- Let the Potatoes Rest: Remove the pot from the heat and allow the potatoes to rest in the cream for 10 minutes.
- Preheat the Oven: Preheat your oven to 375°F (190°C). Grease a 3-quart baking dish with the remaining 2 tablespoons of butter. Remove and discard the thyme sprigs and bay leaves from the potatoes.
- Assemble the Gratin: Using a slotted spoon, transfer half the potatoes into the prepared baking dish. Layer with half the caramelized onions and half the shredded Gruyère cheese.
- Add the Remaining Layers: Top with the remaining potatoes. Pour the remaining cream mixture evenly over the potatoes, then finish with the remaining caramelized onions and Gruyère cheese.
- Bake Until Golden: Bake uncovered for 35–40 minutes, until the cheese is golden and bubbly and the potatoes are fork-tender. If the top browns too quickly, loosely cover with aluminum foil.
- Rest and Serve: Remove from the oven and let rest for 15 minutes before serving. Garnish with fresh thyme if desired. Serve warm and enjoy!
Notes
- Best Potatoes: Russet potatoes work beautifully because their starch helps thicken the creamy sauce. Yukon Gold potatoes are another excellent option.
- Even Slices: Use a mandoline slicer to cut potatoes evenly to ⅛-inch thickness for consistent cooking.
- Don’t Rinse: Avoid rinsing the sliced potatoes, as their natural starch helps create a thicker sauce.
- Caramelized Onions: Cook onions slowly over medium-low heat for the sweetest, richest flavor. Avoid high heat, which can burn them.
- Cheese Substitutions: Replace Gruyère with Swiss cheese, sharp white cheddar, or a combination of mozzarella and Parmesan.
- Make Ahead: Caramelize the onions up to 3 days ahead, or bake the entire gratin a day before serving and refrigerate.
- Storage: Refrigerate leftovers in an airtight container for up to 3–4 days.
- Reheating: Cover with foil and reheat at 350°F (175°C) until thoroughly heated.
- Freezing: Freeze the fully cooked and cooled gratin for up to 2 months for best quality. Thaw overnight in the refrigerator before reheating.
- Serving Suggestion: Pair with roasted chicken, steak, turkey, or a fresh green salad.
- Prep Time: 20 minutes
- Cook Time: 1 hour 35 minutes
- Category: side dish
- Method: Baking
- Cuisine: French-Inspired
Nutrition
- Serving Size: 1/12 of recipe (approximately 300 g)
- Calories: 555 kcal
- Sugar: 6 g
- Sodium: 250 mg
- Fat: 38 g
- Saturated Fat: 24 g
- Unsaturated Fat: 12 g
- Trans Fat: 1 g
- Carbohydrates: 45 g
- Fiber: 3 g
- Protein: 11 g
- Cholesterol: 120 mg