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Au Gratin Potatoes

Au gratin potatoes with thin 1/8-inch slices are layered and baked until the edges are tender and the cheese crust turns bubbling golden. A smooth butter-garlic roux thickens milk and cream into a creamy sauce that clings to every layer.
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Prep Time 25 minutes
Cook Time 1 hour 15 minutes
resting 15 minutes
Total Time 1 hour 55 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French-inspired
Calories: 650
Ingredients Equipment Method Notes

Ingredients
  

Potatoes
  • 3 lb Yukon gold potatoes Peeled and sliced 1/8 inch thick.
Sauce base
  • 3 tbsp butter
  • 3 garlic cloves Minced.
  • 3 tbsp all-purpose flour
  • 2 cup whole milk
  • 1 cup heavy cream
Seasoning
  • 1.5 tsp salt
  • 0.5 tsp black pepper
  • 1 tsp fresh thyme leaves
Cheese
  • 2 cup shredded sharp cheddar Divided (use 1 cup in the sauce and reserve 1 cup for topping).
  • 1 cup shredded Gruyere Divided (use 1/2 cup in the sauce and reserve 1/2 cup for topping).

Equipment

  • 1 sheet pan

Method
 

Preheat and prep the dish
  1. Preheat oven to 375F and butter a 9x13-inch baking dish so the first layer releases easily.
Make the creamy sauce
  1. Melt the butter and cook the minced garlic for 30 seconds, stirring until fragrant.
  2. Whisk in the flour and cook for 1 minute to form a smooth roux without browning.
  3. Slowly whisk in the whole milk and heavy cream, then bring to a simmer and cook until thickened and glossy.
  4. Season the sauce with salt, black pepper, and fresh thyme leaves, stirring until evenly combined.
  5. Remove from the heat and stir in 1 cup of shredded sharp cheddar and 1/2 cup of shredded Gruyere until melted.
Layer and bake
  1. Layer one third of the potato slices in the baking dish and spoon one third of the sauce over the top.
  2. Repeat with a second third of potatoes and sauce, spreading the sauce to the edges for even creamy layers.
  3. Repeat once more with the remaining potatoes and sauce, then top with the remaining cheddar and Gruyere for a browned crust.
  4. Cover with foil and bake for 45 minutes so the potatoes soften through.
  5. Uncover and bake for 25-30 minutes at 375F until golden on top and tender when pierced.
Rest and serve
  1. Rest the au gratin potatoes for 15 minutes before serving, letting the sauce set into thick creamy layers.

Notes

Pro tip: Slice the potatoes to an even 1/8 inch thickness so they cook at the same rate and create uniform creamy layers. Store leftovers covered in the fridge for up to 4 days; reheat in a 350F oven until warmed through. Freezing is not recommended because the dairy can separate when thawed. For a dairy-light swap, use evaporated milk plus a dairy-free cream substitute, but expect a slightly less thick sauce.