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Au Gratin Potatoes

Au gratin potatoes made in a French-inspired layered bake with tender 1/8-inch Yukon gold slices and a thick, thyme-scented cream sauce. Finished with a bubbling cheddar–Gruyère crust and a 15-minute rest for clean, creamy layers.
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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 Peel and slice to about 1/8 inch thick for even layering.
Cheese Sauce
  • 3 tbsp butter For the sauce base and greasing the baking dish.
  • 3 cloves garlic Minced.
  • 3 tbsp all-purpose flour Used to thicken the sauce.
  • 2 cup whole milk Slowly whisked into the flour mixture.
  • 1 cup heavy cream Adds richness to the sauce.
  • 1.5 tsp salt Season to taste in the thickened sauce.
  • 0.5 tsp black pepper Season to taste in the thickened sauce.
  • 1 tsp fresh thyme leaves Fresh leaves for flavor.
  • 2 cup shredded sharp cheddar Divided; 1 cup mixed into the sauce and 1 cup reserved for topping.
  • 1 cup shredded Gruyere Divided; 1/2 cup mixed into the sauce and 1/2 cup reserved for topping.

Equipment

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

Method
 

Prep and heat
  1. Preheat the oven to 375°F and butter a 9x13-inch baking dish for easy release.
  2. Slice the Yukon gold potatoes to about 1/8 inch thick so each layer bakes tender and evenly.
Make the cream cheese sauce
  1. Melt the butter, then cook the minced garlic for 30 seconds until fragrant.
  2. Whisk in the all-purpose flour and cook for 1 minute, stirring to form a smooth paste.
  3. Slowly whisk in the whole milk and heavy cream, then simmer until the mixture thickens to a creamy sauce consistency.
  4. Season the thickened sauce with salt, black pepper, and fresh thyme leaves, then remove from the heat.
  5. Stir in 1 cup shredded sharp cheddar and 1/2 cup shredded Gruyère so the sauce turns glossy and cohesive.
Layer and bake
  1. Layer a third of the sliced potatoes in the baking dish, then spoon over a third of the sauce.
  2. Repeat the potato-and-sauce layering two more times, ending with the last sauce layer.
  3. Top with the remaining shredded sharp cheddar and shredded Gruyère for a golden crust.
  4. Cover with foil and bake for 45 minutes, until the potatoes are beginning to soften and the sauce is bubbling at the edges.
  5. Uncover and bake for 25 to 30 minutes at 375°F until golden and tender, with visible bubbly cheese on top.
Rest and serve
  1. Rest the au gratin potatoes for 15 minutes before serving to set the creamy layers and make slicing easier.

Notes

For the creamiest texture, keep the sauce at a gentle simmer until it thickens before layering—this helps the potatoes absorb liquid without turning watery. Refrigerate leftovers in an airtight container for up to 4 days; reheat covered in a 325°F oven until hot throughout. Freezing is not recommended because the dairy can separate when thawed. For a lighter swap, use half-and-half in place of the heavy cream while keeping the cheddar and Gruyère.