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Au Gratin Potatoes

Au gratin potatoes with thin Yukon gold layers baked in a thickened milk-and-cream sauce for creamy strata and a bubbling golden cheese top. A French-inspired gratin style finished uncovered at 375°F for browned, tender slices.
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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
  

Yukon gold potatoes
  • 3 lb Yukon gold potatoes, peeled and sliced 1/8 inch thick
Butter
  • 3 tbsp butter
Garlic
  • 3 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 shredded sharp cheddar, divided
Gruyere
  • 1 cup shredded Gruyere, divided

Equipment

  • 1 sheet pan

Method
 

Prep and make the cheese sauce
  1. Preheat the oven to 375°F, then butter a 9x13-inch baking dish for easy release. Make sure the dish is evenly buttered at the corners and along the sides.
  2. Melt the butter, add the minced garlic, and cook for 30 seconds. Stop when the garlic is fragrant but not browned.
  3. Whisk in the all-purpose flour and cook for 1 minute. The mixture should look smooth and slightly thickened.
  4. Slowly whisk in the whole milk and heavy cream, then simmer until thickened. Watch for the sauce to coat the back of a spoon and hold a creamy line.
  5. Season the sauce with salt, black pepper, and fresh thyme leaves. Stir until the herbs are evenly distributed.
  6. Remove the sauce from the heat, then stir in 1 cup of the sharp cheddar and 1/2 cup of the Gruyere. Mix until fully melted and glossy.
Layer, bake, and rest
  1. Layer a third of the sliced Yukon gold potatoes in the prepared baking dish, then spoon on a third of the sauce. Spread the sauce to cover the potatoes.
  2. Repeat the layering with another third of the potatoes and another third of the sauce. Tap the dish lightly to help the layers settle.
  3. Add the final third of the potatoes, then pour over the remaining sauce and top with the remaining sharp cheddar and Gruyere. Ensure the top cheese is well scattered for even browning.
  4. Cover with foil and bake for 45 minutes at 375°F. The potatoes should be noticeably tender around the edges.
  5. Uncover and bake for 25 to 30 minutes at 375°F until golden and tender. Look for bubbling cheese and a browned crust across the top.
  6. Rest the au gratin potatoes for 15 minutes before serving. The layers will set and slice more neatly instead of running.

Notes

For the creamiest texture, slice the potatoes to about 1/8 inch and keep your sauce simmer gentle—too hard can make it grainy. Refrigerate leftovers in an airtight container up to 3-4 days; reheat in a 325°F oven until warmed through. Freezing is not recommended because the dairy can separate when thawed. Dietary swap: use lactose-free milk and cream (or lactose-free dairy) to reduce lactose without changing the method.