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Golden caramelized onions over mashed potatoes with melted butter pooling on top, in a deep white serving dish.
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Caramelized Onion & Gruyère Mashed Potatoes

These mashed potatoes are anything but basic, loaded with caramelized onions, Gruyère, and enough butter to cause a scene.
Prep Time15 minutes
Cook Time45 minutes
Total Time1 hour
Course: Side Dish
Cuisine: American
Keyword: caramelized onion and gruyere mashed potatoes, mashed potatoes
Servings: 6
Calories: 393kcal
Author: Joanna Cismaru

Ingredients

  • 3 pounds Yukon Gold potatoes peeled and cubed
  • 1 tablespoon olive oil
  • 2 tablespoons butter divided
  • 2 large yellow onions thinly sliced
  • 1 teaspoon salt plus more for boiling water
  • ½ teaspoon black pepper
  • ⅓ cup whole milk warm
  • ⅓ cup heavy cream warm
  • 1 cup Gruyère cheese shredded
  • Optional: extra butter or chives for serving
US Customary - Metric

Instructions

  • In a skillet, heat olive oil and 1 tablespoon of butter over medium-low heat. Add sliced onions and 1 teaspoon salt. Cook, stirring occasionally, for 25–30 minutes until deep golden brown. Don’t rush it, this is where the flavor happens.
    process shots showing how to make caramelized onion and grueyere mashed potatoes.
  • While the onions cook, place potatoes in a large pot, cover with cold salted water, and bring to a boil. Cook until fork-tender, about 15–20 minutes. Drain well.
    process shots showing how to make caramelized onion and grueyere mashed potatoes.
  • Return drained potatoes to the pot or a large bowl. Add remaining butter, warm milk, and cream. Mash until smooth and fluffy (or leave a few lumps—we're not judging).
    process shots showing how to make caramelized onion and grueyere mashed potatoes.
  • Fold in caramelized onions (reserve a spoonful for topping, if you’re feeling fancy), shredded Gruyère, and black pepper. Taste and adjust seasoning as needed.
    process shots showing how to make caramelized onion and grueyere mashed potatoes.
  • Top with extra caramelized onions, a pat of butter, or a sprinkle of chives if you’re showing off.

Notes

  1. Onions: Low and slow is the rule. Don’t rush it, let them get dark, sweet, and jammy.
  2. Potatoes: Yukon Golds give you naturally creamy texture without needing a science degree or 14 sticks of butter.
  3. Cheese matters: Gruyère adds depth and melty richness. Sharp white cheddar works in a pinch, but you’ll miss that nutty flavor.
  4. Dairy: Warm milk and cream = no gluey mash. Cold dairy = regret.
  5. Make ahead: Totally doable. Reheat low and slow with extra cream or butter stirred in at the end.

Nutrition

Serving: 1serving | Calories: 393kcal | Carbohydrates: 45g | Protein: 13g | Fat: 19g | Saturated Fat: 10g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 6g | Trans Fat: 0.2g | Cholesterol: 51mg | Sodium: 599mg | Potassium: 1082mg | Fiber: 6g | Sugar: 5g | Vitamin A: 548IU | Vitamin C: 48mg | Calcium: 288mg | Iron: 2mg
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