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Au Gratin Potatoes

Au gratin potatoes with thin Yukon gold slices baked until tender in a creamy milk-and-cream sauce, finished with a bubbling golden cheddar–Gruyère crust. Layers are topped with a mix of cheeses for rich, sliceable gratin.
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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: 690
Ingredients Equipment Method Notes

Ingredients
  

Potatoes
  • 3 lb Yukon gold potatoes
Sauce base
  • 3 tbsp butter
  • 3 cloves garlic
  • 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
Cheese
  • 2 cup shredded sharp cheddar divided
  • 1 cup shredded Gruyere divided

Equipment

  • 1 sheet pan
  • 1 Dutch oven

Method
 

Prep and preheat
  1. Preheat the oven to 375F, then butter a 9x13-inch baking dish.
  2. Slice the Yukon gold potatoes into 1/8-inch-thick slices.
Make the creamy sauce
  1. Melt the butter, then cook the minced garlic for 30 seconds.
  2. Whisk in the all-purpose flour and cook for 1 minute.
  3. Slowly whisk in the whole milk and heavy cream, then simmer until thickened.
  4. Season the sauce with salt, black pepper, and fresh thyme leaves.
  5. Remove from the heat and stir in 1 cup shredded sharp cheddar and 1/2 cup shredded Gruyere.
Assemble the gratin
  1. Layer one third of the sliced potatoes and one third of the cheese sauce in the baking dish.
  2. Repeat the potato-and-sauce layers two more times, then top with the remaining cheese (sharp cheddar and Gruyère).
  3. Cover the dish with foil and bake for 45 minutes.
  4. Uncover and bake for 25 to 30 minutes, until golden on top and the potatoes are tender.
  5. Rest the au gratin potatoes for 15 minutes before serving, so the creamy layers set.

Notes

For the creamiest slices, keep potato thickness consistent at about 1/8 inch so everything cooks through at the same pace. Store covered in the refrigerator up to 4 days; reheat individual portions in the microwave or bake covered at 325F until hot. Freezing is not recommended because the sauce can separate after thawing. For a lower-fat swap, use half-and-half instead of heavy cream (texture will be slightly less rich).