Creamy Mashed Potatoes with Caramelized Onions and Horseradish

Caramelized Onion and Horseradish Mashed Potatoes are rich, flavorful mashed potatoes with a gentle spicy lift from prepared horseradish. The sweet, deeply browned onions balance the horseradish’s zing, making this side dish a memorable accompaniment to roasted meats or holiday meals.

I worried at first that the horseradish would be overpowering, but it blends beautifully with Dijon and lemon juice so the heat is subtle — adding brightness without dominating the dish. If you prefer milder flavor, stir in the horseradish a little at a time until the taste is just right for your family.

Ingredients needed:

• 1/4 cup (1/2 stick) butter, divided
• 4 cups chopped onion
• 2 teaspoons brown sugar
• 1 tablespoon white balsamic vinegar (optional)
• 2 1/2 pounds peeled and cubed baking potatoes
• 1/2 cup whole milk
• 1/4 cup Dijon mustard
• 1 tablespoon freshly squeezed lemon juice
• 2 tablespoons prepared horseradish (adjust to taste)
• 1 tablespoon light mayonnaise
• 1/2 teaspoon salt (or to taste)

How to make Caramelized Onion and Horseradish Mashed Potatoes:

The printable recipe with exact measurements appears above in the ingredients list. Follow these steps for smooth, flavorful mashed potatoes.

1. In a medium nonstick skillet, melt 1 tablespoon of butter over medium-high heat. Add the chopped onion and the brown sugar. Sauté, stirring occasionally, for about 10 minutes or until the onions are soft and richly caramelized. If you like a touch of acidity, stir in the white balsamic vinegar after removing the skillet from the heat.
2. Place the peeled and cubed potatoes in a saucepan and cover with cold water. Bring to a boil, then reduce the heat and simmer until the potatoes are tender when pierced with a fork, about 15 minutes depending on the size of the cubes.
3. Drain the potatoes and return them to the pan. Add 3 tablespoons of butter and the whole milk, then mash to your preferred consistency. Continue cooking and stirring for 1–2 minutes to heat through and help the butter and milk meld into the potatoes.
4. In a small bowl, whisk together the Dijon mustard, lemon juice, prepared horseradish, light mayonnaise, and salt until smooth. Taste and adjust the horseradish level if you prefer less or more bite.
5. Fold the Dijon–horseradish mixture and the caramelized onions into the mashed potatoes until evenly combined. Warm gently if needed and transfer to a serving bowl.

These mashed potatoes are not quite the ultra-smooth, velvety style because of the bits of caramelized onion, but that texture is part of their charm. The onions add a sweet, savory depth while Dijon and horseradish brighten the overall flavor.

Serving suggestions

Serve these mashed potatoes alongside roasted or grilled meats, such as roasted chicken, pork, or beef. They also work well with a ladle of gravy for a classic holiday plate. A small pat of butter on top just before serving adds shine and richness.

Variations and tips

• For creamier potatoes, use half-and-half or heavy cream instead of whole milk, adjusting amounts to reach the desired texture.
• If you prefer less horseradish heat, start with 1 tablespoon and increase after tasting.
• Swap yellow or sweet onions for red onions for a slightly different sweetness and color.
• Make the caramelized onions ahead and refrigerate; rewarm and stir into mashed potatoes just before serving.

Notes

• If you need this recipe to be gluten-free, ensure your mayonnaise and prepared horseradish are labeled gluten-free.

Leftovers keep well in an airtight container in the refrigerator for 3–4 days. Reheat gently on the stovetop with a splash of milk to loosen the texture, or warm in the oven covered with foil.