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Au Gratin Potatoes

Au gratin potatoes with thin Yukon gold slices baked in a creamy milk-and-cream sauce until bubbly, golden, and tender. Finished with a sharp cheddar and Gruyère cheese crust and a short 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: 540
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 cloves 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 preheat
  1. Preheat the oven to 375°F, then butter a 9x13-inch baking dish with the butter. Set the dish aside while you make the sauce.
Make the creamy cheese sauce
  1. Melt the butter, then cook the minced garlic for 30 seconds until fragrant. Keep the heat gentle so the garlic doesn’t brown.
  2. Whisk in the all-purpose flour and cook for 1 minute to remove the raw flour taste. The mixture should look smooth and slightly thickened.
  3. Slowly whisk in the whole milk and heavy cream, then simmer until thickened. Visual cue: the sauce should coat a spoon and cling in a creamy layer.
  4. Remove the sauce from heat, then season with salt, black pepper, and fresh thyme leaves. Stir until the herbs are evenly distributed.
  5. Stir in 1 cup sharp cheddar and 1/2 cup Gruyere until fully melted. The sauce should be glossy and smooth.
Layer and bake
  1. Layer a third of the potato slices in the buttered baking dish, then spoon over a third of the sauce. Spread the sauce gently so it reaches the edges.
  2. Repeat the potato-and-sauce layering two more times, using up all potatoes and sauce by the end of the third layer. Visual cue: the dish should be evenly filled with creamy layers.
  3. Top with the remaining sharp cheddar and Gruyère so the surface bakes into a browned crust. Make sure cheese covers most of the top.
  4. Cover the dish with foil and bake for 45 minutes at 375°F. Visual cue: the potatoes should be mostly tender with bubbling sauce under the foil.
  5. Uncover and bake 25 to 30 minutes at 375°F until golden and tender. Visual cue: the top should be deeply golden with active bubbling around the edges.
Rest and serve
  1. Rest the au gratin potatoes for 15 minutes before serving. This helps the creamy layers set so each slice holds together.

Notes

For the creamiest layers, slice the Yukon gold potatoes to an even 1/8-inch thickness so they bake at the same pace. Store leftovers covered in the refrigerator for up to 4 days; reheat in a 325°F oven until warmed through. Freezing is not recommended because the sauce can break when thawed. Dietary swap: use lactose-free milk and cream (or a lactose-free half-and-half) to reduce dairy lactose while keeping the same creamy texture.