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top view potato au gratin in a white dish

Easy Potatoes Au Gratin

Tender sliced potatoes baked to perfect with a creamy sauce made with milk, cheese, garlic, mustard, and onions.
Course Side Dish
Cuisine American, French
Prep Time 15 minutes
Cook Time 1 hour 20 minutes
Total Time 1 hour 35 minutes
Servings 8
Calories 127kcal
Author Rena


  • 2 lb potatoes peeled and thinly sliced
  • Kosher salt and freshly ground black pepper to taste
  • 3 tbsp olive oil divided
  • 1 medium yellow onion thinly sliced
  • 3 garlic cloves minced
  • 1 tbsp wholegrain mustard
  • 3 tbsp gluten-free flour or cornstarch
  • 2 1/2 cups almond milk
  • 1 tsp freshly grated nutmeg or to your taste
  • ¾ cup grated Gruyère cheese
  • Fresh thyme to garnish


  • Preheat the oven to 350F and spray a baking dish with cooking oil spray or olive oil.
  • Add sliced potatoes and season with salt and pepper. Drizzle 2 tbsp oil and toss well to coat. Place in the preheated oven and bake for 15 minutes, or until potatoes begin to soften and the sauce is ready.
  • Meanwhile, heat a rimmed pan over medium heat and drizzle with 1 tbsp oil. Sauté the onion and garlic for 2-3 minutes, or until it softens.
  • Stir in the mustard and flour. Slowly pour the milk and whisk until sauce is thickened and smooth, 2-3 minutes.
  • Season with salt, pepper, and nutmeg.
  • Remove the potatoes from the oven and pour over the sauce, stirring gently to mostly cover and coat.
  • Top with shredded cheese. (You can now cool and refrigerate the dish for make-ahead.)
  • Return to the oven and bake for 60 minutes, or until potatoes are super tender, bubbly, and golden-brown on top. (Cooking time may vary depending on the size of the thickness of your potato slices.)
  • Garnish with fresh thyme before serving.


Oven temperature: Please note that everyone's will be different and cook time will vary. If you try a higher temperature of 400F it will take 35-40 minutes. At 350F it will need 50-60 minutes depending.
Milk: we used almond milk, but you may use any other milk of choice.
Mustard: whole grain mustard was used but you may use dijon mustard
Cheese: If you don't like gruyere or want to use another cheese, consider using a mix of sharp cheddar and parmesan, or gouda.
Potatoes: consider using Yukon gold potatoes 
Flour: Any flour would work for this recipe. Feel free to use cornstarch too. We love to use Whole wheat as well.
Bake time: Don't rush them, they need a good one hour in the oven depending on your oven


Calories: 127kcal | Carbohydrates: 4g | Protein: 5g | Fat: 10g | Saturated Fat: 3g | Cholesterol: 14mg | Sodium: 165mg | Potassium: 35mg | Fiber: 1g | Sugar: 1g | Vitamin A: 117IU | Vitamin C: 1mg | Calcium: 226mg | Iron: 1mg