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Easy Cheesy Potato and Onion au Gratin
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4.82 from 11 votes

Easy Cheesy Potato and Onion Au Gratin

Easy Cheesy Potato and Onion au Gratin is deliciously creamy and a real show stopper. It's a simple side dish that takes minutes to put together, but is packed with cheesy goodness. What's even better is that it can be made ahead of time, and leftovers, if any are just as good the next day. Who could ask for more? 
Prep Time15 mins
Cook Time1 hr 40 mins
Total Time2 hrs
Course: Side Dish
Cuisine: American
Servings: 6 servings
Calories: 445kcal
Author: Chula King


  • 1 onion thinly sliced (about 2 cups)*
  • 5 Tablespoons butter divided
  • 3 Tablespoons all-purpose flour
  • 1 teaspoon salt
  • ¼ teaspoon freshly ground black pepper
  • 2 cups milk
  • 2 cups (8 ounces) shredded Cheddar cheese, divided
  • 2 pounds russet potatoes thinly sliced (about 5 cups)*
  • 3 Tablespoons dry breadcrumbs


  • Preheat oven to 400° F. Butter or spray with vegetable spray a 2-quart casserole dish.
  • Sauté onions in 1 tablespoon of melted butter over medium heat until softened, about 10 minutes. Set aside.
  • In a medium-size saucepan, melt butter over medium heat. Whisk in the flour. Stir constantly with a whisk for one minute. Add milk; whisk until mixture has thickened. Stir in 1 ½ cups of cheese; continue whisking until melted, about 30 to 60 seconds.
  • Layer ½ of the potatoes into bottom of the prepared casserole dish. Top with the sautéed onions and ½ of cheese sauce. Top with the remaining potatoes and remaining cheese sauce.
  • Cover dish and cook 1 hour and 15 minutes in the preheated oven. Remove cover; top with remaining ½ cup of cheese and breadcrumbs. Dot with remaining butter. Return to oven and continue cooking for 15 minutes, or until cheese is melted and potatoes are tender.
  • Yield: 6 servings.


*I used a 2 mm slicing blade on my food processor for slicing both the potatoes and onions.
Note: This can be made ahead of time and reheated. Also, it makes excellent leftovers.


Calories: 445kcal | Carbohydrates: 39g | Protein: 16g | Fat: 25g | Saturated Fat: 15g | Cholesterol: 72mg | Sodium: 784mg | Potassium: 811mg | Fiber: 2g | Sugar: 6g | Vitamin A: 800IU | Vitamin C: 10mg | Calcium: 399mg | Iron: 2mg