The Last Au Gratin Potatoes Recipe You’ll Ever Need Recipe
These creamy au gratin potatoes layer thinly sliced Yukon Golds and tender leeks with Gruyère, Parmesan, and fragrant garlic-thyme cream. Baked until bubbling and golden, this comforting, make-ahead-friendly side dish is perfect for holidays and special dinners.
- Prep Time: 20 minutes
- Cook Time: 1 hour 30 minutes
- Total Time: 1 hour 50 minutes
- Yield: 10 servings
- Category: Side Dish
- Method: Baking
- Cuisine: French-American
- Diet: Vegetarian
Ingredients
For the potato gratin
- 3 pounds Yukon Gold potatoes, sliced ⅛-inch thick
- 2 small leeks, cleaned and thinly sliced (about 1 heaping cup)
- 12 ounces good-melting cheese, such as Gruyère, smoked gouda, or Comté, freshly shredded (about 3 cups)
- 1¼ cups finely grated Parmesan cheese, divided
- Kosher salt and black pepper, to season
- Very soft butter, for greasing the pan
For the thyme cream
- 3½ cups heavy cream
- 10 cloves garlic, smashed and roughly chopped
- 3 tablespoons fresh thyme leaves
Instructions
- Prep the oven and pan.
Preheat the oven to 400°F and position a rack in the center. Generously butter the base and sides of a 9×13-inch baking dish or 4-quart casserole dish; set aside.
- Steep the thyme cream.
Combine the heavy cream, garlic, and thyme in a small saucepan. Bring to a gentle simmer over medium heat and cook for 4–5 minutes, just until fragrant. Remove from the heat and let the mixture steep while you prepare the other ingredients.
- Prepare the potatoes and leeks.
Slice the potatoes about ⅛ inch thick using a mandoline or sharp knife. Trim, clean, and thinly slice the leeks.
- Toss the potato mixture.
In a large bowl, combine the potatoes, leeks, shredded cheese, and ½ cup of the Parmesan. Season with a scant 1 teaspoon kosher salt and a few twists of black pepper. Pour the warm thyme cream over the mixture and toss well, separating any potato slices that stick together so everything is evenly coated.
- Assemble the gratin.
Transfer the mixture to the prepared baking dish, arranging it in even layers and finishing with a layer of potatoes on top. Spoon any remaining cream from the bowl over the gratin. Wipe any drips from the sides of the pan to prevent them from burning.
- Bake covered.
Cover the dish tightly with foil and bake for 60 minutes.
- Finish baking uncovered.
Remove the foil and sprinkle the remaining ¾ cup Parmesan over the top. Return the dish to the oven and bake uncovered for 20–30 minutes, until the top is golden brown and the potatoes are tender when pierced with a fork.
- Rest and serve.
Let the gratin cool for 10–15 minutes so the cream can begin to set. Serve warm.
Notes
- Slice the potatoes evenly, about ⅛ inch thick, so they cook at the same rate. A mandoline makes this easier, but a sharp knife works well.
- Clean the leeks thoroughly, separating the layers to rinse away any trapped grit.
- Choose a cheese that melts smoothly, such as Gruyère, smoked gouda, or Comté.
- Keep the dish tightly covered during the first hour of baking to help the potatoes become tender before browning the top.
- Let the gratin rest for 10–15 minutes before serving; this helps the creamy layers set.
