Sour Cream and Onion Mashed Potato Casserole Recipe (Make-Ahead)

Name: My Make-Ahead Potato Casserole Makes Every Holiday Dinner Easier (and Better)
Prep time: 15 min
Cook time: 60 min
Total time: 75 min
Ingredients: 4 pounds russet potatoes, peeled and cut into 1-inch pieces; Salt to taste; 1 (8-ounce) block sharp cheddar cheese, finely grated (use the small holes on a box grater); 3 tablespoons unsalted butter, divided, plus more for greasing the pan; 2 cups sour cream; 1 bunch scallions (5 to 7 scallions), thinly sliced; 1/2 cup (2 ounces) freshly grated parmesan cheese

A golden, crispy topping adds texture that basic mashed potatoes can’t match.
You can prepare the whole dish days ahead and simply bake it when you’re ready.

Mashed potatoes have never been a favorite of mine. In fact, potatoes are probably my least favorite carb (with the exception of potato chips, which are my FAVORITE carb). I just find most potatoes kind of boring. Phew, glad I got that off my chest!

Now that that’s out of the way, there are many potato dishes I really enjoy. I’ll house a plate of fries (hold the ketchup), and I’ll happily munch on some crispy roasted potatoes with herbs and garlic.

But mashed potatoes, with their lack of exciting flavors and textures, were just never my jam. That is, until one fateful Christmas day, when my mom replaced standard mashed potatoes with this delightfully cheesy, oniony, tangy, crispy-bits-on-top mashed potato casserole.

overhead view of Mashed Potato Casserole in a dish with one serving scooped out onto a plate — Simply Recipes / Photo by Alex Huang / Food Styling by Kaitlin Wayne

Mashed Potatoes, but Better

This amped-up version of classic mashed potatoes has bigger, bolder flavors and a crispy golden brown top that upgrades mashed potatoes in a way you never knew you needed.

The additional prep work—grating cheese and slicing scallions—is minimal and more than compensated for by the fact that this casserole can be fully prepared days in advance and popped into the oven right before dinner.

I highly recommend freshly shredding your cheese rather than buying pre-shredded. Pre-shredded cheese will not melt correctly due to the anti-caking agents added.

Mashed Potato Casserole in a dish with one serving scooped out — Simply Recipes / Photo by Alex Huang / Food Styling by Kaitlin Wayne

Serving Suggestions

This dish quickly became a staple for every major holiday dinner in our family. I would literally beg my mom to make it. While it’s a super versatile side dish, it pairs particularly well with turkey and ham, as the savory onion and tangy sour cream nicely contrast the sweetness of the ham and the mildness of the turkey.

Sour Cream and Onion Mashed Potato Casserole

Prep Time 15 mins

Cook Time 60 mins

Total Time 75 mins

Servings 8 to 10

Yield 3 quarts

This dish is a great make-ahead holiday side. It can be prepped a day or two in advance and refrigerated until ready to cook.

Keep Screen Awake

4 pounds russet potatoes, peeled and cut into 1-inch pieces
Salt to taste
1 (8-ounce) block sharp cheddar cheese, finely grated (use the small holes on a box grater)
3 tablespoons unsalted butter, divided, plus more for greasing the pan
2 cups sour cream
1 bunch green onions (5 to 7 green onions), thinly sliced
1/2 cup (2 ounces) freshly grated parmesan cheese

Cook the potatoes:

If baking immediately, preheat the oven to 375°F.

Place the potatoes in a large pot and cover with cool water by about 2 inches. Salt generously and bring to a boil. Boil until the potatoes are fork-tender, 7 to 10 minutes. Drain the potatoes and return them to the pot, along with the grated cheddar and 2 tablespoons of the butter.
Mash the potatoes:

Mash the potatoes with a potato masher until the butter and cheese are melted and the potatoes are mostly smooth (some lumps are okay). Stir in the sour cream and green onions. Taste and adjust the seasoning with salt.
Assemble the casserole:

Grease a 13 x 9-inch baking dish with nonstick cooking spray or butter. Spread the potatoes evenly in the prepared dish. Cut the remaining 1 tablespoon of butter into small pieces. Top the potatoes with the grated parmesan and dot with the pieces of butter.

If you are preparing the casserole for later, cover tightly with plastic wrap and refrigerate for up to 2 days.
Bake the casserole:

Bake the casserole until the top is lightly golden brown in spots, 40 to 45 minutes. If desired, turn on the broiler and broil until browned to your liking, 1 to 2 minutes more.

If the casserole was refrigerated, remove it from the refrigerator 1 to 2 hours before baking. Bake at 375°F until the top is lightly golden brown in spots, 45 to 60 minutes.

Refrigerate leftovers in an airtight container for up to 5 days. Reheat individual servings in the microwave.

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Nutrition Facts (per serving)
418	Calories
22g	Fat
43g	Carbs
13g	Protein

Nutrition Facts
Servings: 8 to 10
Amount per serving
Calories	418
% Daily Value*
Total Fat 22g	28%
Saturated Fat 12g	61%
Cholesterol 64mg	21%
Sodium 348mg	15%
Total Carbohydrate 43g	16%
Dietary Fiber 4g	16%
Total Sugars 4g
Protein 13g
Vitamin C 17mg	87%
Calcium 297mg	23%
Iron 2mg	12%
Potassium 1113mg	24%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.

Nutrition information is calculated using an ingredient database and should be considered an estimate. In cases where multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.