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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 with a garlic-thickened milk sauce, then finished uncovered for tender potatoes and browned cheese.
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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: 580
Ingredients Equipment Method Notes

Ingredients
  

Potatoes and baking dish
  • 3 lb Yukon gold potatoes peeled and sliced 1/8 inch thick
  • 3 tbsp butter for buttering the baking dish and building the sauce base
Garlic-thickened milk sauce
  • 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
Cheese layer
  • 2 cup shredded sharp cheddar divided
  • 1 cup shredded Gruyere divided

Equipment

  • 1 sheet pan

Method
 

Prep and preheat
  1. Preheat oven to 375F, then butter a 9x13-inch baking dish.
Make the sauce
  1. Melt butter, then cook minced garlic for 30 seconds.
  2. Whisk in all-purpose flour and cook for 1 minute.
  3. Slowly whisk in whole milk and heavy cream, then simmer until thickened.
  4. Season the sauce with salt, black pepper, and fresh thyme leaves.
  5. Remove from heat and stir in 1 cup shredded sharp cheddar and 1/2 cup shredded Gruyere.
Assemble the gratin
  1. Layer a third of the sliced Yukon gold potatoes and a third of the sauce in the baking dish.
  2. Repeat layering two more times with the remaining potatoes and sauce, ending with a final layer of sauce.
  3. Top with the remaining shredded sharp cheddar and shredded Gruyere, creating an even cheese cap (visual cue: fully covered surface).
Bake and rest
  1. Cover with foil and bake for 45 minutes.
  2. Uncover and bake 25 to 30 minutes until golden and tender (visual cue: bubbling edges and browned cheese).
  3. Rest 15 minutes before serving (visual cue: layers set and sauce slightly thickens).

Notes

Pro tip: slice the potatoes consistently at about 1/8 inch so they bake tender in the same time window. Refrigerate leftovers in an airtight container for up to 3 days; reheat covered in a 325F oven until warmed through. Freezing is not recommended because the creamy sauce can separate when thawed. For a lighter option, use half-and-half instead of heavy cream for a similar creamy texture with less richness.