Au Gratin Potatoes
This au gratin potatoes recipe layers 2 pounds of paper-thin Yukon Gold slices with a Gruyère and cheddar sauce, then finishes under a panko and Parmesan crust for a creamy, cheesy, and crisp side dish.
Equipment
- Mandoline slicer - For uniform 1/8-inch potato slices
- Chef's knife - For dicing the onion and mincing the garlic
- 2-quart baking dish - An 8x8-inch (20 cm) or 9x9-inch (23 cm) dish
- Heavy-bottomed saucepan - 3 quarts works well, for the roux and sauce
- Whisk - For a lump-free sauce
- Box grater - For shredding the Gruyère and cheddar
- Rimmed baking sheet - To catch any bubbling sauce
- Aluminum foil - For covering the dish during the first bake
- Small bowl - For the topping
Ingredients
For the potatoes and sauce
- 2 pounds Yukon Gold potatoes - 900 g, about 6 medium, peeled and sliced 1/8 inch (3 mm) thick
- 5 tablespoons unsalted butter - 70 g, divided (3 tablespoons for the sauce, 1 tablespoon for greasing the dish, 1 tablespoon melted for the topping)
- 1 small yellow onion - about 1/2 cup or 75 g, finely diced
- 2 cloves garlic - minced
- 3 tablespoons all-purpose flour - 24 g
- 1 1/2 cups whole milk - 360 ml
- 1 cup heavy cream - 240 ml
- 1 teaspoon kosher salt
- 1/2 teaspoon freshly ground black pepper
- 1/4 teaspoon whole nutmeg - freshly grated
- 1 teaspoon fresh thyme leaves
- 1 1/2 cups Gruyère cheese - 6 oz or 170 g, shredded, divided (1 cup for the sauce, 1/2 cup for the topping)
- 1 cup sharp cheddar cheese - 4 oz or 113 g, shredded, divided (3/4 cup for the sauce, 1/4 cup for the topping)
For the topping
- 1/2 cup panko breadcrumbs - 30 g
- 1/4 cup Parmigiano-Reggiano - 25 g, finely grated
- 1 tablespoon fresh parsley - chopped, for garnish
Instructions
- Move an oven rack to the middle position and preheat the oven to 375°F (190°C). Grease the bottom and sides of an 8x8-inch or 9x9-inch baking dish with 1 tablespoon of the butter and set it on a rimmed baking sheet.
- Peel the potatoes and slice them 1/8 inch (3 mm) thick on a mandoline. Keep the slices together in a large bowl and do not rinse them.
- Shred the Gruyère and cheddar. Combine 1 cup Gruyère and 3/4 cup cheddar for the sauce, and the remaining 1/2 cup Gruyère and 1/4 cup cheddar with the Parmigiano-Reggiano and panko for the topping.
- Melt 3 tablespoons butter in a heavy 3-quart saucepan over medium heat. Cook the onion for 4 to 5 minutes until soft and translucent, then stir in the garlic and cook for 30 seconds.
- Whisk in the flour for 1 to 2 minutes, then slowly pour in the milk while whisking. Whisk in the cream and bring to a gentle bubble, then simmer for 3 to 4 minutes until thickened. Off the heat, stir in the salt, pepper, nutmeg, thyme, and sauce cheese until smooth.
- Layer one-third of the potatoes in the dish, top with one-third of the sauce, and repeat twice more. Press down gently with a spatula so the layers sit flat.
- Cover the dish tightly with foil and bake for 45 minutes, until the sauce is bubbling around the edges.
- Toss the melted butter with the topping mixture and scatter it evenly over the surface. Bake uncovered for 25 to 30 minutes, until deeply golden and a knife slides through the potatoes easily.
- Let the dish rest for 15 minutes, sprinkle with parsley, and cut into 8 portions.
Notes
- Slice the potatoes evenly at 1/8 inch for the best texture; a mandoline makes this easy.
- Yukon Golds are ideal because they hold their shape while turning creamy.
- Do not rinse the potato slices; the surface starch helps thicken the sauce.
- Shred your own cheese for a smoother sauce, as pre-shredded cheese can be grainy.
- Add the cheese off the heat to prevent a greasy or grainy sauce.
- Whisk the milk in slowly to avoid lumps.
- Season the sauce slightly well, as the potatoes absorb a lot of salt.
- Keep the foil tight during the first bake so the steam cooks the potatoes through.
- Never skip the 15-minute rest; it lets the sauce set for clean portions.
- Make ahead: assemble through step 6, cover, and refrigerate up to 24 hours; bake covered for 55 to 60 minutes before adding the topping.
- Store leftovers in the refrigerator for up to 4 days and reheat gently, covered, at 350°F (175°C).
- Freeze baked portions for up to 2 months; the texture may become slightly grainy after thawing.
Nutrition
Serving: 1ServingCalories: 460kcalCarbohydrates: 27gProtein: 16gFat: 32gSaturated Fat: 19gSodium: 570mgFiber: 2gSugar: 4g
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