Garlic Parmesan Mashed Potato Casserole

Garlic Parmesan Mashed Potato Casserole makes the PERFECT Thanksgiving and holiday side dish! Creamy russet potatoes are cooked with garlic cloves, then mashed with butter, milk and parmesan cheese. Top with additional parmesan before baking to create a crispy exterior on this comforting casserole. Makes 8 large servings.

Need something to pair this casserole with? Check out Browned Butter Sage Turkey and Brioche Bread Stuffing Recipe!

This post first appeared at Julie’s Eats and Treats, where I was a contributor.

A close up of Garlic Parmesan Mashed Potato Casserole, shown in a purple baking dish with a serving spoon

The night I made this casserole for the first time, my husband declared, “I think those are the best mashed potatoes you’ve ever made.”

And y’all, this is something coming from him because the man is not really a mashed potato fan.

In fact, he’s the great grandson of a rice farmer, so their family always ate rice with dinner.

For him to be on board with a mashed potato dish is kind of a Big Deal.

Why I love this recipe:

This Garlic Parmesan Mashed Potato Casserole is my new favorite potato dish, too, because it is so very simple to make.

It also packs a ton of flavor into the potatoes and works as a side dish for a weeknight meal, as well as a holiday like Thanksgiving or Christmas.

No matter when you serve this mashed potato casserole, it’s gonna be well-loved!

And the best news is Garlic Parmesan Mashed Potato Casserole can and should be made in advance so you don’t have to fret about it the day of!

I’ll tell you exactly how to do this a little farther down in this post, as well as in the recipe card. Promise.

Other make-ahead Thanksgiving sides our whole family adores: Creamed Cornbread CasseroleBourbon Sweet Potato CasseroleFresh Green Bean CasseroleDrunken Cranberry Sauce

Searching for Thanksgiving recipes that save the day every time? Check out my BEST Thanksgiving Recipes recipe index!

Potatoes are shown sitting on a grey polka dot towel on an aqua background

What do I need to make this recipe?

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Let’s talk ingredients!

In addition to the tools above, you’re going to need some ingredients to make this recipe, too! Chances are, you might already have some of them in your fridge or pantry. Scroll down to the recipe card for the full measurements and instructions.

Here’s what you need:

  • Russet potatoes—russets have a lot of starch, and they will break down as we boil the potatoes, which is what we want.
  • Garlic cloves—or granulated garlic, if you’re unsure if you’d like the garlic cooked with the potatoes
  • Kosher salt—or another medium-grain salt
  • Unsalted butter—you can also use salted butter if that’s what you’ve got on hand. If you make this swap, leave out the salt and give the potatoes a taste before seasoning.
  • Whole milk—while you can use another milk in this recipe, I really advise the whole milk because it will make the potatoes more flavorful.
  • Parmesan cheese—use your favorite parmesan. We like to shred our own, but I know the pre-shredded stuff can be a lot easier!
  • Black pepper
Collage showing how to make mashed potato casserole

How to make Garlic Parmesan Mashed Potato Casserole

First and foremost, scrub the potatoes!

Next, peel the potatoes using a vegetable peeler. 

Once peeled, chop into 1″ cubes using a sharp knife.

Why? Because the smaller the cubes, the less time it’ll take for them to get soft. 

Make the mashed potatoes

Fill a large pot with cold water. Add the potatoes and garlic to the water. Season with salt, and turn on the flame. (Don’t add potatoes to boiling water because they will cook unevenly.)

Bring to a boil over high heat, and cook until the potatoes are tender. This should take around 20 minutes, depending on your burner.

When the potatoes are tender, drain in a colander, and then put them back into the saucepan. Leave the garlic in, too, because that’s going to add immense flavor!

Measure the butter, milk and 1 cup of parmesan cheese on top of the potatoes.

Use a hand mixer or a potato masher to combine the ingredients until creamy and smooth (or your desired consistency if you like a chunkier potatoes.)

Season with salt and pepper.

Bake the casserole

Preheat the oven, and spray a baking dish with nonstick cooking spray.

Transfer the creamy mashed potatoes into the prepared dish.

Sprinkle the additional cheese on top of the casserole.

Bake for 25 minutes, then turn up the heat for an additional 15 minutes. This final 15 minutes in the higher heat is going to melt and brown the cheese.

When the cheese is all bubbly, remove the casserole from the oven, and let it cool slightly.

If you’re making this on a holiday, and it needs to come out of the oven earlier, cover it with aluminum foil so it retains some heat!

Serve warm, and enjoy.

mashed potato casserole in a blue baking dish

Erin’s Easy Entertaining Tips

I loooooooooove casseroles for entertaining because they’re super easy to make in advance and super easy to store and reheat. 

They’re also delicious.

Here are a few of the things I’ve learned about this mashed potato casserole over the years that might help you as you make it to entertain your people:

  • Make it in advance. You can put this casserole together 2-3 days beforehand, and keep the dish covered in the fridge before you bake it on the day of your event.
  • Leave out the garlic if you don’t like it (or if your guests don’t, too). We adore garlic in our house because garlic adds amazing flavor… but I know not everyone’s tastebuds are like ours. If you’re skeptical or worried about using garlic, leave it out, and sprinkle some granulated garlic into the mashed potatoes along with the salt and pepper once you’ve whipped them up. Go by taste, and make your measurements confidently.
  • Keep it warm. This is a dish that you can make 1-2 hours in advance and cover with aluminum foil to ensure it stays warm. You don’t want it to be scorching hot when you serve it, so covering it will do the trick for a little bit!
A serving of the potatoes is served on a white plate

Frequently Asked Questions

What is the best way to mash the potatoes?

Personally, I like to use a hand mixer* (affiliate link) to make the mashed potatoes super smooth.

The potatoes should be soft enough that they can very easily blend with the other ingredients.

When the potatoes are fork tender, drain, then toss them back in the saucepan (or Dutch oven) with the butter, milk and parmesan. Blend slowly with the hand mixer and pick up speed as the ingredients meld together. Blend until whipped and silky smooth.

Does this recipe use leftover mashed potatoes?

If you happen to have 3 lbs. of mashed potatoes leftover, sure! Depending on how they were made, you might need to add a little more milk, butter, parmesan and garlic.

With the garlic, I suggest cooking it in a pan with some olive oil or butter before throwing it into the potatoes so it’s not completely raw since raw garlic has a more potent taste than cooked.

Can I make this Mashed Potato Casserole ahead of time?

YES! In fact, I advise doing this because it makes life easier.

Make the mashed potatoes a day or two before the big day, and transfer them into a baking dish. (You won’t cover them in cheese or bake now—that’ll come the day of!) All you’ll do now is cover them with plastic wrap, then store in the fridge.

The day of, unwrap the casserole dish, top with cheese and bake until the cheese is golden, brown, bubbly and delicious.

Can I make this casserole at home and transport it to another location without too much drama?

YES! This dish would be awesome to transport and quite easy to finish at someone else’s house.

Follow the instructions laid out about making the dish in advance. Bring it covered in plastic wrap, and once there, top with cheese and bake until bubbly and delicious.

I don’t like fresh garlic. Can I use granulated garlic instead?

Sure! I know fresh garlic can be a little strong for some, so if you want to make the swap, do it. I would start with ½ teaspoon of the granulated garlic. Taste it for flavor, and add more if you want more garlic flavor.

What are some other potato dishes that I might enjoy?

Now who’s ready to make this life changing, make ahead mashed potato casserole?

A close up of Garlic Parmesan Mashed Potato Casserole, shown in a purple baking dish with a serving spoon
Yield: 8 large servings

Garlic Parmesan Mashed Potato Casserole

Prep Time: 15 minutes
Cook Time: 1 hour
Total Time: 1 hour 15 minutes

Garlic Parmesan Mashed Potato Casserole makes the PERFECT Thanksgiving and holiday side dish! Creamy russet potatoes are cooked with garlic cloves, then mashed with butter, milk and parmesan cheese. Top with additional parmesan before baking to create a crispy exterior on this comforting casserole. No matter if you're serving the family for a holiday or on a weeknight, Garlic Parmesan Mashed Potato Casserole packs a flavorful punch for any meal!

Ingredients

  • 3 lbs. russet potatoes, scrubbed, peeled and diced into 1” cubes
  • 5 garlic cloves, whole
  • 1 teaspoon kosher salt, (to season put in water for the diced potatoes)
  • 4 tablespoons unsalted butter
  • 1 cup whole milk
  • 1 ¾ cups parmesan cheese, shredded and divided
  • 1 teaspoon black pepper, freshly ground
  • ½ teaspoon kosher salt

Instructions

  1. Using a sharp knife, chop the scrubbed and peeled potatoes into 1” cubes.
  2. Fill a large saucepan or Dutch oven with water, then add the potatoes to the water. Place the garlic cloves in the water, as well.
  3. Season the water with a teaspoon of salt.
  4. On the stovetop, heat the water and potatoes over high heat and bring to a boil. Cook until the potatoes are fork tender, about 20 minutes.
  5. Drain the potatoes, and place back in the saucepan.
  6. Measure out the butter, milk and 1 cup of parmesan cheese on top of the potatoes.
  7. Using a hand mixer on a low speed, slowly blend the ingredients together until smooth and creamy. Season the potatoes with salt and pepper.
  8. Preheat the oven to 350°F. Spray a baking dish with nonstick cooking spray, and set aside.
  9. Transfer the mashed potatoes into the prepared baking dish. Sprinkle the additional ¾ cup cheese on top of the casserole.
  10. When the oven is preheated, transfer the casserole to the oven.
  11. Bake for 25 minutes, then turn up the heat to 425°F. Bake for an additional 15 minutes, or until the cheese has browned.
  12. Remove from the oven, and let cool slightly.
  13. Serve warm, and enjoy!

Notes

Make Ahead Tip: Make the mashed potatoes a day or two before the big day, and transfer them into a baking dish. (You won’t cover them in cheese or bake now—that’ll come the day of!) All you’ll do now is cover them with plastic wrap, then store in the fridge.

The day of, unwrap the casserole dish, top with cheese and bake until the cheese is golden, brown, bubbly and delicious.

Nutrition Information:

Yield:

8

Serving Size:

1 serving

Amount Per Serving: Calories: 311Total Fat: 12gSaturated Fat: 7gTrans Fat: 0gUnsaturated Fat: 4gCholesterol: 31mgSodium: 731mgCarbohydrates: 39gFiber: 4gSugar: 4gProtein: 12g

Nutrition facts are an estimate and not guaranteed to be accurate.

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