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Cheesy Mashed Potatoes Casserole

A savory make ahead cheesy mashed potato casserole that's easy to double or triple, making your holiday cooking to-do's a whole lot easier!
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Prep Time: 20 minutes
Cook Time: 35 minutes
Total Time: 55 minutes
Course: Side Dish
Cuisine: American
Keyword: best cheesy mashed potatoes, cheddar cheese mashed potatoes, cheddar mashed potatoes, cheesy mashed potatoes, cheesy mashed potatoes casserole, cheesy mashed potatoes recipe, cheesy mashed potatoes with sour cream, easy cheesy mashed potatoes, make ahead mashed potatoes, make ahead mashed potatoes casserole, make mashed potato, steak and potatoes
Servings: 8 servings
Calories: 294kcal
Cost: $0.87 per serving

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  • 8 x 8-inch or 9 x 9-inch casserole dish


Ingredients for Cheesy Mashed Potatoes Casserole

  • 4 pounds russet potatoes
  • Kosher salt for salting the potato water
  • 2 tablespoons chives fresh, chopped
  • 1 bunch scallions chopped, white and green parts separated
  • 1/2 cup + 1 tablespoon unsalted butter brought to room temperature, divided
  • 1 cup sour cream brought to room temperature
  • 1 cup cheese any kind, shredded


The Method

  • If planning to bake immediately, preheat oven to 350°F. Butter an 8 x8-inch or a 9 x9-inch casserole with 1 tablespoon of the butter. Set aside.
  • Peel and quarter the potatoes and add them to a large stock pot. Add enough COLD tap water to cover by 1/2-inch. Sprinkle with Kosher salt, about 1/2 tablespoon.
  • Bring the pot to a boil and boil the potatoes for about 15 minutes or until a fork will stab them without resistance.
  • Melt the butter. Using a hand mixer or a potato masher, add to the potatoes and mash coarsely. They need not be smooth yet. Add the sour cream. Mash until smooth. DO NOT overwork the potatoes.
  • Fold the chopped chives, dry-cured ham or prosciutto if using, and the green parts of the scallions into the mashed potatoes, along with the shredded cheese. Spoon the mixture into the prepared casserole dish. Scatter the remaining white parts of the scallions over the top.

You can bake the casserole now or cover and refrigerate for a later bake.

  • To bake the casserole immediately, place into the preheated oven and bake for 20 minutes or until top is lightly golden and scallions are beginning to brown.
    If baking the casserole at a later time, pull it from the refrigerator and let it stand for 10 minutes while the oven preheats. Place into the oven and bake for 30 to 35 minutes or until lightly golden and scallions are beginning to brown.


Please Note that table salt and iodized salt are NOT substitutions for Kosher salt. Do not use table salt or iodized salt in any of the recipes you find on Not Entirely Average UNLESS specified otherwise.
To Freeze:
For a whole casserole, assemble the recipe following the directions stopping just before baking it. Assemble in a freezer safe glass baking dish with a tight fitting lid or with a double layer of aluminum foil. After marking with the contents and the date of freeze on the outside, place flat into the freezer. Freeze for up to three months.
For freezing leftover portions which have already been baked, spoon into a freezer safe plastic container with a tight-fitting lid, then mark with the contents and date of freeze noted on the container. Freeze for up to three months.
To thaw and heat: 
Place in the refrigerator over night.
To heat a whole casserole, once completely thawed, bake as directed on the recipe card as it will be being baked for the first time.
For previously baked portions, heat gently in the microwave until hot.


Serving: 1serving | Calories: 294kcal | Carbohydrates: 42g | Protein: 9g | Fat: 11g | Saturated Fat: 6g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 3g | Trans Fat: 1g | Cholesterol: 30mg | Sodium: 123mg | Potassium: 1011mg | Fiber: 3g | Sugar: 2g | Vitamin A: 390IU | Vitamin C: 14mg | Calcium: 166mg | Iron: 2mg

Please note that the nutrition information provided above is approximate and meant as a guideline only.