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A Mashed Potato Casserole with a golden, crispy topping and sliced green onions, partially served in a white oval dish.

Mashed Potato Casserole

I love making this Mashed Potato Casserole because it's creamy, cheesy, and has the most incredible golden crust on top. The sour cream keeps the potatoes smooth and adds a subtle tang, while the Cheddar melts into every bite for rich, savory flavor. The crispy fried onions and breadcrumb topping create the perfect balance to the creamy base underneath. I make this for Thanksgiving, Christmas, holiday potlucks, and cozy family dinners because it's easy to prep ahead and always disappears fast. It will stay fresh in the fridge for 3 to 4 days or freeze well for up to 3 months.
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Prep Time: 20 minutes
Cook Time: 55 minutes
Total Time: 1 hour 15 minutes
Course: casserole, Dinner, Side Dish
Cuisine: American
Keyword: Mashed Potato Casserole
Servings: 10
Calories: 422kcal
Author: Mandy Applegate

Equipment

Ingredients

  • 4 pounds russet potatoes peeled and cut into chunks
  • 2 cups Cheddar cheese shredded
  • 1 cup milk
  • 1 cup sour cream
  • ½ cup unsalted butter
  • 1 teaspoon garlic powder
  • 1 teaspoon onion powder
  • Salt and black pepper to taste

Toppings:

  • ¼ cup chopped green onions
  • 2 tablespoons breadcrumbs
  • 1 cup crispy fried onions
US Customary - Metric

Instructions

  • Set the oven to 375°F (190°C) and butter a 9 × 13-inch baking dish.
  • Place the potato chunks in a large pot of generously salted water. Bring to a boil and cook for 20 to 25 minutes, or until the potatoes are fork-tender. Drain well.
    4 pounds russet potatoes
  • Transfer the drained potatoes to a large mixing bowl. Mash until smooth and lump-free using a potato masher or an electric mixer.
  • Stir in the butter, milk, sour cream, garlic powder, onion powder, half of the shredded Cheddar cheese, and salt and black pepper. Mix until creamy and well blended.
    2 cups Cheddar cheese, 1 cup milk, 1 cup sour cream, ½ cup unsalted butter, 1 teaspoon garlic powder, 1 teaspoon onion powder, Salt and black pepper
  • Spread the mashed potato mixture evenly into the prepared baking dish. Sprinkle the remaining Cheddar cheese and breadcrumbs evenly over the top.
    2 tablespoons breadcrumbs
  • Place the dish in the oven and bake for 25 to 30 minutes, or until the top is golden brown and the cheese is melted.
  • Let the casserole rest for 5 minutes. Garnish with crispy fried onions and chopped green onions before serving.
    ¼ cup chopped green onions, 1 cup crispy fried onions

Video

[adthrive-in-post-video-player video-id="KNQemOgd" upload-date="2025-11-14T09:13:31+00:00" name="Easy Homemade Mashed Potato Casserole" description="Soft, buttery potatoes baked into the perfect holiday or weeknight side." player-type="default" override-embed="default"]

Notes

Here are my tried-and-true tips for making this mashed potato casserole turn out perfect every time:
Drain the potatoes thoroughly: After boiling, let them sit in the colander for a full minute to steam off excess moisture. Watery potatoes mean a watery casserole that won't hold its shape.
Don't overmix the potatoes: Once you add the dairy ingredients, mix just until combined. Overworking the potatoes activates too much starch and makes them gummy instead of fluffy. You can use Yukon Golds for extra creaminess.
Use room temperature dairy: Let your butter, milk, and sour cream sit out for 30 minutes before mixing. Cold dairy can make the potatoes seize up and turn gluey. You can also swap half the milk for heavy cream for a silkier texture.
Adjust cheese to your taste: If you want it extra cheesy, add another half cup of Cheddar to the potato mixture. For a milder version, use sharp white Cheddar instead of the orange variety, or fontina for a more buttery flavor.
Add crispy bacon for extra richness: Crumble 6 to 8 strips of cooked bacon into the mashed potato mixture before baking, or sprinkle it on top with the fried onions for a smoky, savory crunch that takes this casserole over the top.
Store properly: Store leftovers in an airtight container in the fridge for 3 to 4 days or freeze portions for up to 3 months. Reheat in the oven or microwave until warmed through, adding a splash of milk if needed.

Nutrition

Calories: 422kcal | Carbohydrates: 40g | Protein: 11g | Fat: 25g | Saturated Fat: 14g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 5g | Trans Fat: 0.4g | Cholesterol: 64mg | Sodium: 237mg | Potassium: 858mg | Fiber: 3g | Sugar: 3g | Vitamin A: 720IU | Vitamin C: 11mg | Calcium: 246mg | Iron: 2mg
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