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Au Gratin Potatoes

Au gratin potatoes with thin, creamy layers and a bubbling golden cheese crust. Baked in a buttered dish at 375°F until tender, then rested for clean, sliceable servings.
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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: 620
Ingredients Equipment Method Notes

Ingredients
  

Potatoes
  • 3 lb Yukon gold potatoes, peeled and sliced 1/8 inch thick
Dairy and seasonings
  • 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

Method
 

Prep and make the sauce
  1. Preheat your oven to 375°F and butter a 9x13-inch baking dish. Use even coverage so the top browns without sticking.
  2. Melt the butter, then cook the minced garlic for 30 seconds. Stop when fragrant, but not browned.
  3. Whisk in the all-purpose flour and cook for 1 minute. Keep whisking until smooth and lightly bubbling.
  4. Slowly whisk in the whole milk and heavy cream, then simmer until thickened. Stop when the sauce coats the back of a spoon.
  5. Season the sauce with salt, black pepper, and fresh thyme leaves. Stir until evenly speckled and fragrant.
  6. Remove from heat and stir in 1 cup of the sharp cheddar and 1/2 cup of the Gruyere. Mix until the cheeses melt and the sauce turns glossy.
Layer and bake
  1. Layer one third of the potatoes in the baking dish and spoon one third of the sauce over them. Spread to cover the surface so the layers cook evenly.
  2. Repeat with a second third of the potatoes and a second third of the sauce. Tap the dish lightly to settle the slices.
  3. Finish with the remaining potatoes and pour the remaining sauce over the top. Make sure the top is mostly covered by creamy sauce.
  4. Sprinkle the remaining sharp cheddar and Gruyere on top. Aim for an even layer so it bakes into a cohesive crust.
  5. Cover with foil and bake for 45 minutes. Look for bubbling around the edges before uncovering.
  6. Uncover and bake for 25 to 30 minutes, until golden and tender. Watch for a browned, bubbling cheese top and soft potato slices.
Rest and serve
  1. Rest for 15 minutes before serving. The layers will set so each slice holds together cleanly.

Notes

For the creamiest texture, slice potatoes to about 1/8 inch and keep the sauce thick enough to coat a spoon before layering. Store covered in the refrigerator for up to 4 days; reheat in a 350°F oven until hot throughout. Freezing is not recommended because the creamy sauce can break after thawing. If you need a lower-fat option, use evaporated milk plus half-and-half in place of the whole milk and heavy cream.