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Au Gratin Potatoes

Au gratin potatoes with thin Yukon Gold slices baked in a creamy milk-and-cream sauce and finished with a bubbling golden cheddar–Gruyère crust. French-inspired, layered for tender bites and a thick, velvety cheese sauce in every scoop.
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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: 520
Ingredients Equipment Method Notes

Ingredients
  

Potatoes
  • 3 lb Yukon gold potatoes peeled and sliced 1/8 inch thick
Creamy sauce base
  • 3 tbsp butter
  • 3 clove garlic minced
  • 3 tbsp all-purpose flour
  • 2 cup whole milk
  • 1 cup heavy cream
  • 1.5 tsp salt
  • 0.5 tsp black pepper
  • 1 tsp fresh thyme leaves
Cheeses
  • 2 cup shredded sharp cheddar divided
  • 1 cup shredded Gruyere divided

Equipment

  • 1 sheet pan
  • 1 9x13-inch baking dish

Method
 

Preheat & prep dish
  1. Preheat oven to 375°F, then butter a 9x13-inch baking dish so the potatoes release easily after baking.
Make the creamy sauce
  1. Melt the butter in a saucepan, then cook the minced garlic for 30 seconds until fragrant.
  2. Whisk in the all-purpose flour and cook for 1 minute to form a smooth roux with no dry spots.
  3. Slowly whisk in the whole milk and heavy cream, then simmer until thickened, stirring to keep the sauce glossy.
  4. Season the thickened sauce with salt, black pepper, and fresh thyme leaves, and stir until evenly distributed.
  5. Remove from heat and stir in 1 cup shredded sharp cheddar and 1/2 cup shredded Gruyère until melted and smooth.
Layer & bake
  1. Layer one third of the sliced potatoes and one third of the sauce in the prepared baking dish.
  2. Repeat the layering two more times with the remaining potatoes and sauce, then top with the remaining sharp cheddar and Gruyère.
  3. Cover with foil and bake 45 minutes to soften the potatoes and set the creamy base.
  4. Uncover and bake 25 to 30 minutes until golden on top and the potatoes are tender.
Rest & serve
  1. Rest the au gratin potatoes for 15 minutes before serving so the sauce thickens into creamy layers.

Notes

For the best sliceable layers, keep the potato thickness around 1/8 inch so they finish tender at the same time. Cover with foil for the first bake to prevent cheese from scorching, then uncover to brown. Store in the refrigerator up to 3-4 days; reheat in a 325°F oven until hot. Freezing is not recommended because the cream sauce can break after thawing. For a gluten-free option, use a 1:1 gluten-free all-purpose flour blend for the roux.