Caramelized onion and horseradish mashed potatoes are creamy, tangy, spicy and sweet. Rich and creamy mashed potatoes paired with spicy horseradish and sweet caramelized onions. They’re the perfect side dish for your Thanksgiving spread!

caramelized onion and horseradish mashed potatoes in bowl with forks and napkin

Horseradish is the Nordic equivalent to the chili pepper. It’s a popular, spicy condiment can be served with meat, fish, or beets. You can add it to potato salad, on vegetables, in a bloody Mary or anything else you want!

These mashed potatoes combine the sweetness from the caramelized onions, the spiciness from the horseradish, the tanginess from the Dijon with the creaminess of the potatoes (and all the butter of course!). They have so much more flavor than plain old mashed potatoes (not that there’s anything wrong with regular mashed potatoes!). You’ll love this new twist on an old favorite!

Ingredients & Substitutions

Caramelized onions and horseradish mashed potatoes ingredients

Potatoes: I generally use russet potatoes, which are great because of their high starch content. Yukon Golds are another great option because of their buttery texture.
Onions: I use sweet onions which are sweeter than other varieties impart a natural sweetness, but you can caramelize almost any type of onion – yellow, white, red.
Butter: I use unsalted butter so I can control the amount of added salt. If you’re using salted butter, adjust the amount of added salt to taste.
Whole milk: Whole milk makes the potatoes extra creamy. You can use cream if that’s what you have available. Remember to warm the dairy.
Dijon mustard: Adds a little tanginess to the potatoes.
Prepared horseradish: Horseradish has a spicy and pungent flavor. It adds a nice kick to the potatoes. You can adjust to your preference by adding more or using less.
Salt: To enhance the flavors.

How To Make Caramelized Onion and Horseradish Mashed Potatoes

Caramelize the onions

Melt the butter in a large skillet over medium heat.
Once the butter has melted, add the onions to the skillet and cook for 5-10 minutes, stirring frequently, until the onions soften.
Reduce the heat to medium-low, add the salt, and continue to cook. Stir them every 5 minutes or so. You don’t want to stir them too often because they need to be in contact with the pan in order to brown, but you also don’t want them to burn. If the onions are looking dry add a little more fat or a splash of liquid like water or stock.
Continue cooking for 45-60 minutes, or until they turn a deep brown color. The exact cook time will vary depending on the size of your pan, the size and age of the onions and the heat from your stove.

make the mashed potatoes

Make the mashed potatoes while the onions are cooking. Peel and cut the potatoes into 1-inch chunks.
Place potatoes in a large stockpot or Dutch oven and fill the pot so the water line is about 1 inch above of the potatoes and season with 1 Tbsp salt.
Bring to a boil over high heat, then turn the heat down to medium-high and gently boil for 10-12 minutes, or until you can easily insert a knife into the center of the potatoes with very little resistance.
Drain the potatoes and immediately return the potatoes back to the hot stockpot and return it to the hot burner. Turn heat down to low.
Using two oven mitts or potholders, grab the handles of the pot and shake it on the burner for about 1 minute to dry up any residual moisture in the pot.
Remove the pot from the burner and place it on a heat proof surface.
Mash the potatoes using your tool of choice. I find a ricer makes a fluffy mashed potato without mixing them too much and making them gluey.

riced potatoes in pot with caramelized onions and horseradish

mashed potatoes in pot mixed with caramelized onions and horseradish

Heat the butter and milk until the butter has just melted. This can also be done in the microwave or in a small saucepan on the stove. Be careful not to boil the milk.
Add milk, butter, caramelized onions, Dijon and horseradish to potatoes. Stir to combine. Don’t overmix the potatoes or they’ll get gummy.
Taste and add salt as needed.

caramelized onion and horseradish mashed potatoes in bowl with napkin

Expert Tips

Use a ricer – A ricer will give you light and fluffy mashed potatoes without overmashing them. Potatoes are mostly starch, and when starch is handled too much it becomes gummy and gluey. No one wants that!
Warm the milk and butter – Hot potatoes don’t absorb cold liquids very well. Cold liquids will also cool down the potatoes which is not the goal. So warm up the milk and butter so the potatoes absorb all that creamy goodness.
Drain and dry the potatoes – Once the potatoes have cooked, drain and return them to the burner to dry up any residual moisture. This helps prevent soggy, watery mashed potatoes.

Can I Make This Ahead of Time?

You can caramelize the onions the day before making the potatoes. I usually do that when I’m making these mashed potatoes. Store them in a sealed container in the refrigerator for a day or two.

Mashed potatoes are best served when fresh and warm so I wouldn’t recommend making the potatoes ahead of time.

How to Store Caramelized Onion and Horseradish Mashed Potatoes

Store these mashed potatoes in a sealed container in the refrigerator for 3-4 days.

How To Reheat Caramelized Onion and Horseradish Mashed Potatoes

Here are my favorite ways to reheat the mashed potatoes. I usually reheat them in the microwave because that’s the quickest and I don’t want to wait to dig into delicious mashed potatoes! Add a splash of cream or milk and a pat of butter when reheating so the potatoes don’t dry out. Microwave at half power for a minute, then stir. Continue microwaving in 30 second intervals until the potatoes are heated through.

They can also be reheated in the oven. Transfer the potatoes to a baking dish, add some cream and butter, cover and bake at 350ºF for about 15-20 minutes, or until the potatoes are heated through.

What To Serve with Caramelized Onion and Horseradish Mashed Potatoes

These potatoes are so versatile and can be eaten as a side dish or on their own.

They’re delicious with my Swedish meatballs and gravy!
They pair wonderfully with meats like roast beef, tenderloin or prime rib.
Try them with my Danish breaded pork patties (karbonader).
They pair perfectly my easy refrigerator pickled beets recipe or my Swedish beetroot salad (rödbetssallad).
I like to have them for breakfast with a fried egg on top.

More Side Dish Recipes You’ll Love

Caramelized Onion and Horseradish Mashed Potatoes

Caramelized onion and horseradish mashed potatoes made with creamy mashed potatoes, spicy horseradish and sweet caramelized onions.

5 from 3 votes

Print Recipe Pin Recipe

Prep Time 15

Cook Time 50

Total Time 1 5

Servings

Ingredients

For the caramelized onions

2 yellow onions, medium
2 Tbsp butter, unsalted
pinch of salt

For the mashed potatoes

2 lbs russet potatoes (4-6 medium), peeled and cut into 1-inch chunks
4 Tbsp butter, unsalted (½ stick), melted
2/3 cup whole milk, warmed
1 Tbsp Dijon mustard
2 Tbsp prepared horseradish
salt, to taste

Instructions

Make the caramelized onions:

Melt the butter in a large skillet over medium heat.
Once the butter has melted, add the onions to the skillet and cook for 5-10 minutes, stirring frequently, until the onions soften.
Reduce heat to medium-low, add the salt, and continue to cook, stirring every few minutes. If the onions are looking dry add a little more fat or a splash of liquid like water or stock.
Continue cooking for 45-60 minutes, or until they turn a deep brown color. Exact cook time will vary depending on the size of your pan, the size and age of the onions and the heat from your stove.

Make the mashed potatoes

While the onions are cooking, peel and cut the potatoes into 1-inch chunks.
Place potatoes in a large stockpot or Dutch oven and fill the pot so the water line is about 1 inch above of the potatoes. Season with 1 Tbsp salt.
Bring to a boil over high heat, then turn the heat down to medium-high and gently boil for 10-12 minutes, or until you can easily insert a knife into the center of the potatoes with very little resistance.
Drain potatoes and immediately return to the hot stockpot. Return to the hot burner and turn heat down to low.
Using two oven mitts or potholders, grab the handles of the pot and shake it on the burner for about 1 minute to dry up any residual moisture in the pot.
Remove the pot from the burner and place it on a heat proof surface.
Mash the potatoes using your tool of choice.
Heat butter and milk until the butter has just melted. Be careful not to boil the milk.
Add milk, butter, caramelized onions, Dijon and horseradish to potatoes. Stir to combine. Don't overmix the potatoes or they'll get gummy.
Taste and add salt as needed.

Notes

Use a ricer – A ricer will give you light and fluffy mashed potatoes without overmashing them. Potatoes are mostly starch, and when starch is handled too much it becomes gummy and gluey. No one wants that!

Warm the milk and butter – Hot potatoes don’t absorb cold liquids very well. Cold liquids will also cool down the potatoes which is not the goal. So warm up the milk and butter so the potatoes absorb all that creamy goodness.

Drain and dry the potatoes – Once the potatoes have cooked, drain and return them to the burner to dry up any residual moisture. This helps prevent soggy, watery mashed potatoes.

Nutrition

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