Why It Works
- Steeping the milk and cream with aromatics adds extra flavor.
- Slicing the potatoes directly into hot milk releases starches into the milk mixture, resulting in a creamier gratin.
- Baking the gratin uncovered allows the milk and cream to reduce and break into silky curds.
- Allowing the gratin to rest before serving gives the potatoes time to absorb the rich dairy.
After rounds and rounds of testing, we've finally landed on the perfect classic potato gratin (also known as scalloped potatoes or au gratin potatoes), one that's creamy, silky, and loaded with flavor. To make it, thinly sliced russet potatoes are layered with earthy Gruyère and nutty-sweet Parmesan before being slowly baked in a bubbling bath of milk and cream. Going low-and-slow in the oven gently reduces the milk and cream, which breaks and coagulates into creamy curds within the layers of potato. A final blast under the broiler browns the top and yields a crispy golden crust.
- 1 cup (240ml) heavy cream
- 2 cups (480ml) whole milk
- 2 medium cloves garlic (8g), smashed
- 2 small shallots (110g total), quartered
- 1/8 teaspoon freshly grated nutmeg
- 6 sprigs fresh thyme
- 2 teaspoons (6g) whole black peppercorns
- 1 1/2 teaspoons (7g) Diamond Crystal kosher salt
- 3 large russet potatoes (about 30 ounces; 800g)
- 2 ounces (60g) grated Parmigiano-Reggiano cheese
- 4 ounces (120g) grated Gruyère cheese
- 1 tablespoon (15g) unsalted butter, softened
In a small saucepan, combine cream, milk, garlic, shallots, nutmeg, thyme, peppercorns, and salt. Bring to a boil, then remove from heat, cover, and let steep for 1 hour.
Return milk mixture to boil, then strain into a large heatproof bowl, pressing gently on the solids.
Using a mandoline, slice the potatoes crosswise 1/8 inch thick, directly into the hot milk mixture. Stir the potatoes to fully coat.
Preheat oven to 300°F (150°C). In a small bowl, combine the Gruyère and Parmigiano-Reggiano cheeses.
Grease a 2-quart baking dish with the butter. Lay the sliced potatoes in one even layer, then sprinkle with the cheese mixture. Repeat layering potatoes and cheese until all the potatoes have been used and half the cheese mixture remains; leave the top layer without cheese. Pour any remaining milk mixture over the layered potatoes.
Bake until the potatoes have become tender and the surface is lightly golden brown, about 1 1/2 hours. Top with reserved cheese mixture, switch the oven to broil, and broil until evenly browned on top. Allow the gratin to rest 30 minutes before serving.