Classic Potato Gratin
You don't need flour or butter roux to thicken a gratin. The starch released from the sliced potatoes as they bake in the oven does the heavy lifting, turning simple cream into a rich, velvety binder.
Don't wash the potatoes after slicing.
The starch on the surface of the slices is essential for the thickening process. Keep your knife or mandoline work consistent so the layers cook through at the same rate.
- Mandoline or sharp chef's knife
- Large mixing bowl
- 2-quart shallow baking dish
- Aluminum foil
What goes in.
- 3 lbYukon Gold potatoes, peeled and sliced 1/8-inch thick
- 2 cupsheavy cream
- 1 cupwhole milk
- 2 clovesgarlic, smashed and minced
- 1 tspkosher salt
- 1/2 tspfreshly cracked black pepper
- 1/4 tspfreshly grated nutmeg
- 1 cupGruyère cheese, finely grated
The Dry-Slice Method
Slice your potatoes directly into a dry bowl. If you soak them in water, you rinse away the natural thickener required to turn your cream and milk into a cohesive custard.
The method.
Heat the oven and prep the dish
Preheat your oven to 375°F (190°C). Rub the interior of your baking dish with a cut clove of garlic, then smear a thin layer of butter over the bottom and sides.
Season the liquid
In a medium bowl, whisk together the cream, milk, minced garlic, salt, pepper, and nutmeg.
Layer the potatoes
Arrange the potato slices in the dish, overlapping them like shingles. Pour the cream mixture over the potatoes, pressing down gently so the liquid rises just to the top layer.
First bake
Cover the dish tightly with aluminum foil. Bake for 45 minutes until the potatoes are tender when pierced with a paring knife.
Finish with cheese
Remove the foil, sprinkle the Gruyère evenly over the top, and return to the oven uncovered for another 20 to 25 minutes. The gratin is done when the top is golden brown and the edges are bubbling vigorously.
Rest
Let the dish stand on the counter for at least 15 minutes before serving to allow the sauce to set.
Other turns to take.
Herbed Crust
Add one tablespoon of finely minced fresh thyme or rosemary to the cream mixture before pouring it over the potatoes.
Allium Base
Sauté a thinly sliced leek in butter until soft and spread it along the bottom of the dish before adding the first layer of potatoes.
When it doesn't go to plan.
Use a mandoline for the most consistent thickness, which ensures even cooking.
If the top browns too quickly, tent a piece of foil loosely over it until the final 10 minutes.
Never serve straight from the oven; the layers need to settle or the structure will collapse into a puddle.
The ones that keep coming up.
Can I use Russet potatoes instead?
Russets are very high in starch and tend to break down into a mealy texture rather than holding their shape. Yukon Golds or similar waxy varieties yield a better result.
Why did my sauce curdle?
Curdling usually happens if the oven temperature is too high or if the dairy content is too low in fat. Stick to heavy cream and milk combinations as specified to ensure stability.