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Au Gratin Potatoes

Au gratin potatoes with thin Yukon gold slices baked in a creamy garlic béchamel until bubbly, golden, and tender. Layered with sharp cheddar and Gruyère for classic French-inspired au gratin texture and a crisp cheese crust.
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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: 610
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 sharp cheddar shredded, divided
Gruyere
  • 1 cup Gruyere shredded, divided

Equipment

  • 1 sheet pan

Method
 

Prep and preheat
  1. Preheat oven to 375F, then butter a 9x13-inch baking dish. Set aside while you make the sauce so the dish is ready to layer.
  2. Melt butter in a saucepan over medium heat. Keep it moving until fully melted and glossy.
  3. Cook minced garlic for 30 seconds in the butter. Look for a fragrant aroma without browning.
  4. Whisk in all-purpose flour and cook for 1 minute. Stir constantly until the roux looks smooth and lightly thickened.
  5. Slowly whisk in whole milk and heavy cream. Keep whisking until the mixture simmers and thickens, then stop whisking and allow gentle bubbling.
  6. Season the thickened sauce with salt, black pepper, and fresh thyme leaves. Taste and ensure herbs are evenly distributed.
  7. Remove the sauce from heat and stir in 1 cup sharp cheddar and 1/2 cup Gruyere. Mix until the cheeses melt and the sauce turns silky.
Layer and bake
  1. Layer a third of the sliced Yukon gold potatoes and a third of the sauce in the prepared dish. Spread into an even layer so the potatoes cook through uniformly.
  2. Repeat with another third of the potatoes and another third of the sauce. Tap the dish lightly on the counter to settle the layers.
  3. Repeat once more with the remaining potatoes and the remaining sauce, then top with the remaining sharp cheddar and Gruyere. The surface should be fully covered with cheese.
  4. Cover the dish with foil and bake for 45 minutes at 375F. You should see bubbling around the edges once the sauce has worked its way up.
  5. Uncover and bake for 25-30 minutes at 375F until golden and tender. Look for a browned, bubbling cheese crust and potatoes that offer no resistance.
Rest and serve
  1. Rest the au gratin potatoes for 15 minutes before serving. This sets the creamy layers so each slice holds together.

Notes

Pro tip: keep potato slices close to 1/8 inch so they cook tender at the same time as the sauce thickens. Store leftovers covered in the refrigerator up to 3-4 days; reheat in a 325F oven until hot throughout. Freezing is not recommended because the creamy dairy can break when thawed. For a dairy swap, use lactose-free whole milk and lactose-free heavy cream to keep the same thick, creamy texture.