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Potatoes Au Gratin

The best Potatoes Au Gratin recipe combines thinly sliced potatoes and a creamy flavorful cheese sauce that gets baked to perfection with a crispy top.
Course Side Dish
Cuisine American
Prep Time 20 mins
Cook Time 55 mins
Total Time 1 hr 15 mins
Servings 8 servings
Calories 323


  • 3 pounds golden potatoes (lightly scrubbed, skin on, and sliced thin, see note)
  • 1 medium yellow onion (peeled and sliced thin)
  • 4 tablespoons unsalted butter
  • 4 tablespoons all-purpose flour
  • 2 cups whole milk
  • 4 cloves roasted garlic (smashed into paste)
  • 1 teaspoon dry mustard
  • ¼ teaspoon nutmeg (freshly grated )
  • 2 cups cheddar cheese (shredded (I used a cheddar gruyere blend))
  • 1 teaspoon Kosher salt (or more, to taste)
  • ½ teaspoon pepper ( freshly ground)


  • Preheat oven to 400 degrees F.
  • Wash potatoes and slice into thin slices. Soak in large bowl of cold water for at least an hour.
  • Melt butter in a sauce pan and add sliced onion. Stir to coat in butter and then allow to cook, undisturbed, until the onion starts to brown. Add the flour and cook 2-3 minutes, stirring constantly to avoid burning. You want mixture to smell like a cooked pie crust. Add milk and whisk over medium heat until thick and bubbly. Remove from heat and stir in roasted garlic, dry mustard, nutmeg, and cheese until melted.
  • Place potato slices upright in a greased casserole dish. Sprinkle with salt and pepper. Spoon cheese sauce over potatoes.
  • Cover with greased lid or foil and bake 35 minutes, covered. Remove cover and bake an additional 20-30 minutes or until lightly browned and potatoes are cooked.


  • A mandolin is the easiest way to get super thin sliced potatoes.
  • The thinner your potatoes, the faster they will cook. If you do not slice with a mandolin, you may have to increase your cooking time. Likewise, if potatoes are not of uniform thickness, the thin slices will cook much faster than the thick slices.


Calories: 323kcal | Carbohydrates: 29g | Protein: 14g | Fat: 17g | Saturated Fat: 11g | Cholesterol: 51mg | Sodium: 511mg | Potassium: 837mg | Fiber: 5g | Sugar: 4g | Vitamin A: 557IU | Vitamin C: 21mg | Calcium: 331mg | Iron: 6mg