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.

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.

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 in a bit. Promise.)

Other make-ahead Thanksgiving sides our whole family adores: Creamed Cornbread Casserole | Bourbon Sweet Potato Casserole | Fresh Green Bean Casserole | Drunken Cranberry Sauce

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

What tools do I need to make this Garlic Parmesan Mashed Potato Casserole?

Disclaimer: The links below are affiliate links. If you click through and take action, I will receive a small commission. Please refer to my disclosure page for more information about the affiliate programs The Speckled Palate participates in. 

• Vegetable peeler
• Saucepan
• Liquid measuring cup
• Hand mixer
• Box grater
• Baking dish

How to make Garlic Parmesan Mashed Potato Casserole

First and foremost, scrub those potatoes! Like, really good because you don’t want any dirt on ’em.

Next, peel the potatoes using a vegetable peeler. 

Once peeled, chop them using a sharp knife into 1″ cubes. Why? Because the smaller the cubes, the less time it’ll take for them to get soft. 

Make the mashed potatoes

Fill a large saucepan or a Dutch oven with cold water. Add the chopped potatoes and garlic cloves to the water. Season the water with salt, and then turn on the flame. (You don’t want to add your potatoes to water that’s already boiling because they will cook unevenly.)

Heat the water, potatoes and garlic over high heat. Bring ’em to a boil, and cook until the potatoes are fork tender. This should take around 20 minutes, depending on how high your burner goes.

When the potatoes are fork 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 to the potatoes!

Measure in the butter, milk and 1 cup of parmesan cheese on top of the potatoes. Use a hand mixer on a low speed to blend the ingredients together until creamy and smooth. Season ’em with salt and pepper after tasting, too!

You can also do this manually, though it will take more time. If you are going to do it this way, I suggest smashing the potatoes with a fork before stirring in the other ingredients and trying to get them as smooth as possible. That said, lumpy potatoes aren’t pretty, but they don’t taste bad. 😉 

Bake the casserole

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

Transfer the creamy mashed potatoes into the prepared baking dish. Sprinkle the additional cheese on top of the casserole.

Bake ’em for 25 minutes, then turn up the heat some more for an additional 15 minutes. This final 15 minutes in the higher heat is going to get the cheese all melty and browned and delicious.

When the cheese is all bubbly and delicious, 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!

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 super delicious, too.

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 casserole 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!

Frequently Asked Questions

What is the best way to mash the potatoes?

Personally, I like to use a hand mixer to make the mashed potatoes super smooth and creamy.

The key is making sure the potatoes are soft enough that they can very easily blend them up 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. Start blending slowly with the hand mixer and pick up speed as the ingredients meld together. Blend until the potatoes are whipped and smooth and the perfect silky consistency.

Does this recipe use leftover mashed potatoes? Or can I substitute them in for the fresh mashed potatoes?

If you happen to have 3 lbs. of mashed potatoes leftover, absolutely! 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.

When we plan our dishes for Thanksgiving, my family and I try to make as many as possible in advance. 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 people, so if you want to make the swap with granulated garlic, 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 if I like this one, too?

• Mediterranean Scalloped Potatoes
• Mashed Yuca (in case you want a potato-y dish without the potatoes! These would be a brilliant substitution for the potatoes in this recipe)
• Bourbon Butter Sweet Potatoes
• Loaded Mashed Potato Casserole
• Vegan Scalloped Potatoes

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

Scroll on down to learn how simple it is to make…

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

Are you a mashed potato or a rice person? 

Could I interest you in a serving of this Garlic Parmesan Mashed Potato Casserole today?

The photos and recipe for this Garlic Parmesan Mashed Potato Casserole were originally published on November 19, 2018. The text of this blog post was updated and republished on November 13, 2019.