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Au Gratin Potatoes

Au gratin potatoes with thinly sliced Yukon golds baked in a garlic-thickened milk and cream sauce until bubbling and golden. Layered for creamy, tender slices and a browned cheese crust.
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Prep Time 25 minutes
Cook Time 1 hour 15 minutes
rest 15 minutes
Total Time 1 hour 55 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French-inspired
Calories: 620
Ingredients Equipment Method Notes

Ingredients
  

Yukon gold potatoes
  • 3 lb Yukon gold potatoes peeled and sliced 1/8 inch thick
butter
  • 3 tbsp butter
garlic
  • 3 clove garlic minced
all-purpose flour
  • 3 tbsp all-purpose flour
whole milk
  • 2 cup whole milk
heavy cream
  • 1 cup heavy cream
salt
  • 1.5 tsp salt
black pepper
  • 0.5 tsp black pepper
fresh thyme leaves
  • 1 tsp fresh thyme leaves
sharp cheddar
  • 2 cup sharp cheddar shredded, divided (use 1 cup in sauce, reserve 1 cup for topping)
Gruyere
  • 1 cup Gruyere shredded, divided (use 1/2 cup in sauce, reserve 1/2 cup for topping)

Equipment

  • 1 sheet pan

Method
 

Prep the dish
  1. Preheat the oven to 375F. Butter a 9x13-inch baking dish so the potatoes release easily.
Make the creamy sauce
  1. Melt the butter in a saucepan and cook the minced garlic for 30 seconds, stirring until fragrant. You should see light bubbling around the garlic.
  2. Whisk in the all-purpose flour and cook for 1 minute, stirring constantly to remove the raw flour taste. The mixture should look smooth and slightly thick.
  3. Slowly whisk in the whole milk and heavy cream, then bring to a simmer. Simmer until thickened, with a slow, creamy coat on the whisk.
  4. Season the sauce with salt, black pepper, and fresh thyme leaves, then stir to combine. The color should stay creamy and speckled with thyme.
  5. Remove the saucepan from heat and stir in 1 cup sharp cheddar and 1/2 cup Gruyere. Mix until the cheese melts and the sauce looks glossy.
Layer and bake
  1. Layer a third of the sliced Yukon gold potatoes in the baking dish. Press them into an even thickness for consistent doneness.
  2. Pour a third of the cheese sauce over the potatoes, spreading to the edges. Add a thin, even layer so the slices steam together.
  3. Repeat with another third of potatoes and another third of sauce, then do the same once more. The top layer should be potatoes with sauce just underneath.
  4. Sprinkle the remaining sharp cheddar and Gruyere over the top layer. Use an even coverage so you get a uniformly browned crust.
  5. Cover the dish with foil and bake for 45 minutes at 375F. The sauce should be visibly bubbling around the edges.
  6. Uncover and bake for 25-30 minutes at 375F until golden and tender. Look for a browned, bubbling cheese surface.
Rest and serve
  1. Rest the au gratin potatoes for 15 minutes before serving. The layers should set slightly so slices hold together.

Notes

For the creamiest texture, keep potato slices at about 1/8 inch so they bake evenly through. Store leftovers covered in the refrigerator for up to 4 days; reheat in a 325F oven until hot throughout. Freezing is not recommended because the dairy may separate after thawing. If you need a dairy-light option, use low-fat milk and a reduced amount of heavy cream, but expect a slightly less rich sauce.