Au Gratin Potatoes
These Au Gratin Potatoes are a rich, cheesy potato casserole made with Yukon gold potatoes, onion, Cheddar, Gruyere, and Parmesan. They bake until creamy in the center and golden on top, making them perfect for holidays or family dinners.
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Servings: 8
Ingredients
Potatoes
- 2 1/2 lbs Yukon gold potatoes sliced into 1/8-inch rounds
- 1/2 medium yellow onion thinly sliced
Sauce
- 3 tbsp salted butter
- 1/4 c all-purpose flour
- 1 1/2 c whole milk or unsweetened almond milk
- 8 oz sharp Cheddar cheese shredded
- 3/4 tsp kosher salt plus more to taste
- 1/2 tsp garlic powder
- Freshly ground black pepper to taste
Toppings
- 2 oz Gruyere cheese shredded
- 2 oz Parmesan cheese grated
- Chopped fresh chives or parsley
Instructions
- Preheat the oven to 375°F. Lightly coat a 9-inch square baking dish with cooking spray.
- Arrange the sliced potatoes in the prepared baking dish in three or four slightly overlapping rows. The slices should be slightly slanted, not tightly packed. Distribute the onion slices between and over the potatoes.
- To prepare the sauce, melt the butter in a medium saucepan over medium heat. Whisk in the flour and cook for approximately 30 seconds, whisking constantly, until a smooth paste forms.
- Gradually pour in the milk, whisking continuously to prevent lumps from forming. Increase the heat to medium-high and bring the mixture to a boil. Reduce the heat to medium-low and simmer, stirring occasionally, until the sauce thickens to a creamy consistency, about 5 minutes.
- Reduce the heat to low. Stir in the Cheddar cheese, kosher salt, garlic powder, and several grinds of black pepper. Taste and adjust the seasoning with additional salt and pepper if needed.
- Pour the cheese sauce evenly over the arranged potatoes and onions. Cover the dish tightly with foil.
- Bake for 45 minutes.
- Remove the foil and sprinkle the Gruyere and Parmesan evenly over the top.
- Return the dish to the oven and bake uncovered for 30 to 45 minutes, or until the potatoes are tender when pierced with a fork and the top is golden brown.
- For a more deeply browned topping, place the dish under the broiler on high for 1 to 2 minutes, watching closely to prevent burning.
- Allow the dish to rest for 10 minutes. Garnish with chopped chives or parsley before serving.
Notes
To make these Au Gratin Potatoes gluten free, replace the all-purpose flour in the sauce with a gluten-free all-purpose flour blend or an equal amount of cornstarch slurry added after the milk is heated. You should also confirm that the cheeses, seasonings, and cooking spray are labeled gluten free, since anti-caking agents and additives can vary by brand. The potatoes, onion, butter, and milk are naturally gluten free, but if cross-contact is a concern, prepare the dish with clean utensils, a clean baking dish, and ingredients that have not been exposed to gluten-containing foods.