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.

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 and 

It also packs a ton of flavor into the potatoes and works as the perfect side dish for a special occasions, whether it’s a holiday meal OR a big family dinner. This is also lovely as a weeknight side dish, too.

No matter when you serve this mashed potato casserole, it’s gonna be well-loved because it is the ULTIMATE comfort food.

Please note that this is not a classic mashed potato casserole recipe, so you won’t find ingredients like sour cream, cream cheese, fresh chives or green onions here, but this is a fun twist on the classic.

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 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 do I need to make this recipe?

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

Here’s what you need:

• Potatoes — russet potatoes have a lot of starch, and because of this, they are the best potatoes for this recipe. They will break down as we boil them, which is what we want. I do not recommend using Yukon gold potatoes or pre-made mashed potatoes in this dish.
• Garlic cloves — or granulated garlic / garlic powder, 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

Substitutions and additions:

• Swap the parmesan for shredded cheddar cheese. ​
• Mix crunchy panko bread crumbs with the shredded cheese for extra crunchiness in the topping.
• Add crispy bacon for a meaty crunch to the topping.

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

To do this, we are going to follow my Homemade Mashed Potatoes recipe, but make them extra creamy. 

First, 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 fork tender.

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.

Please note that you can use leftover mashed potatoes here if you’ve got enough! 

Bake the casserole

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

Transfer the creamy mashed potato mixture into the prepared dish. 

Sprinkle the additional shredded cheese on top.

Bake uncovered 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. The baking time is dependent on your oven, so keep an eye on the dish, especially near the end so it does not burn.

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.

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!

Frequently Asked Questions

Quick tips and tricks for the best potato casserole:

• Cook the mashed potatoes in advance, ​and assemble the casserole early, especially if you’re making this to serve as a side for Thanksgiving dinner, Christmas dinner or even a big family dinner.
• Have fun with the flavors. ​If you like different cheese, give that a try!
• How to store: Cover with foil or plastic wrap in the fridge and store for up to 5 days. If you have a smaller amount of casserole and want to remove it from the casserole dish, store in an airtight container.

More potato recipes to try:

• Mediterranean Scalloped Potatoes
• Homemade Mashed 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
• Hasselback Sweet Potatoes
• Vegan Scalloped Potatoes

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