French Onion Mashed Potatoes

These French Onion Mashed Potatoes take everything you love about a bowl of French onion soup (sweet, jammy caramelized onions and melted Gruyère) and fold it right into buttery, creamy mashed potatoes. They’re rich, cozy and seriously hard to stop eating!

Marrying into a French family changed the way I think about potatoes. My husband grew up watching his family cook traditional French dishes, and his grandmother’s Potato gratin dauphinois is still one of the most comforting things I know how to make. These mashed potatoes borrow that same love of cream, cheese and simple ingredients cooked with care.

The secret here is patience with the onions. Cooking them low and slow for over an hour turns them deeply golden and sweet, and that’s where all the French onion soup flavor comes from. It’s a labor of love, but you can make the onions ahead, which makes this a perfect side for holidays and Sunday dinners.

Why You’ll Love This French Onion Mashed Potatoes Recipe

• All the flavor of French onion soup. Sweet caramelized onions, melty Gruyère and a hint of thyme turn simple mashed potatoes into something special. It’s comfort food at its finest.
• Ultra creamy and buttery. Yukon gold potatoes, heavy cream and plenty of butter make these mashed potatoes rich and silky. No gummy, gluey texture here.
• Holiday-worthy side dish. They’re impressive enough for Thanksgiving or Christmas dinner, but easy enough for a Sunday roast. Everyone will ask for the recipe.
• Make-ahead friendly. The caramelized onions can be cooked days in advance, and the finished potatoes reheat beautifully. That’s a big win when your stovetop is crowded.
• Naturally gluten-free. There’s no flour in this recipe, so it’s a great side for guests who avoid gluten.

Ingredient Notes

• Unsalted butter: Used in three stages, for caramelizing the onions, warming the cream and finishing the mash. Unsalted butter lets you control the salt.
• Yellow onions: They have the perfect balance of sweetness and savory flavor for caramelizing. Slice them thinly and evenly so they cook at the same rate.
• Yukon gold potatoes: Naturally buttery and creamy, they mash up smooth without getting gluey. You’ll need about 8 to 10 potatoes. You can also use russet potatoes.
• Salt: Seasoning the cooking water and the finished mash makes sure the potatoes are flavorful all the way through.
• Heavy whipping cream: Makes the potatoes extra rich and velvety. Warming it first helps it absorb smoothly.
• Ground thyme: Adds that classic, earthy French onion soup flavor.
• Garlic powder: Gives a mellow garlic flavor that blends evenly into the cream.
• Gruyère cheese: Nutty, slightly sweet and melty, it’s the traditional cheese on French onion soup. Shred it from a block for the smoothest melt.
• Black pepper: Adds a little warmth and balances the richness.
• Fresh parsley (optional): A sprinkle on top adds color and a fresh finish.

Variations & Substitutions

• Swiss or Comté cheese: Swap the Gruyère for Swiss, Emmental or Comté for a similar nutty flavor.
• Fresh thyme: Use about 1 1/2 teaspoons fresh thyme leaves instead of the ground thyme.
• Fresh garlic: Replace the garlic powder with 2 to 3 minced garlic cloves, simmered in the butter and cream.
• Lighter version: Use half-and-half or whole milk instead of heavy cream.
• Dairy-free: Use a plant-based butter, unsweetened oat or soy cream, and a dairy-free melting cheese.
• Gluten-free: This recipe is naturally gluten-free as written.

Tips for Success

• Don’t rush the onions. True caramelized onions need time and gentle heat to turn deep golden brown and jammy. If you crank up the heat, they’ll burn on the outside before they have a chance to sweeten.
• Cut the potatoes evenly. Keeping the cubes roughly the same size helps them cook at the same rate. That way you won’t end up with some pieces mushy and others still firm in the middle.
• Use warm cream and butter. Adding warm liquid helps the potatoes absorb it quickly and stay fluffy. Cold cream cools the potatoes down and can leave them dense and lumpy.
• Mash by hand and don’t overdo it. A potato masher gives you the best texture, while a blender or food processor will overwork the starch. Mash just until smooth to keep the potatoes light and fluffy instead of gluey.

Serving Suggestions

Serve these French onion mashed potatoes warm, topped with the reserved caramelized onions, a little extra Gruyère and a sprinkle of fresh parsley. They’re a dream next to a holiday roast like my Lemon and thyme roasted turkey or a Latin-style Pavo a lo criollo.

For a cozy Sunday dinner, pair them with Apple cider roasted pork loin and some roasted green beans, then finish the meal with a slice of Easy French apple cake.

Storage Suggestions

• Refrigerator: Store leftover mashed potatoes in an airtight container for up to 4 days.
• Reheat in the oven: Transfer to a baking dish, cover with foil and bake at 350°F until heated through, stirring halfway.
• Freezer: Freeze in an airtight container for up to 2 months. Thaw overnight in the fridge and reheat with a little extra cream, since they may look slightly grainy at first.

Frequently Asked Questions

Do I have to peel the potatoes?

No. Peeling the potatoes will create a smoother texture, but you can certainly leave them unpeeled if you prefer a more rustic style mashed potatoes.

Why do my mashed potatoes turn gluey?

Gluey mashed potatoes happen when they’re overworked, which releases too much starch. Mash by hand just until smooth, and avoid using a blender or food processor.

Can I caramelize the onions faster?

To properly caramelize onions, it’s important to cook them slowly at low heat. Otherwise you risk burning the onions. The onions’ flavor will be well worth the time spent! You can speed things up slightly with a pinch of salt and a splash of water when they start to stick, but real caramelization takes time. Cooking them over high heat will brown them, but they won’t get that sweet, jammy flavor.

Can I make French onion mashed potatoes ahead of time?

Yes, these are a great make-ahead side for the holidays. Make them up to 2 days ahead, refrigerate, then reheat on the stove or in the oven with a splash of cream.

French Onion Mashed Potatoes

Recipe for French Onion Mashed Potatoes, these homemade creamy mashed potatoes are mixed with sweet caramelized onions and Gruyère cheese for that ultimate comfort food flavor.

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Course: Side Dish

Cuisine: French inspired, Fusion, International

Keyword: Caramelized onions, Comfort food, Gruyère cheese, Mashed potatoes

Prep Time: 25 minutes minutes

Cook Time: 1 hour hour 15 minutes minutes

Total Time: 1 hour hour 40 minutes minutes

Servings: 10

Ingredients

• ½ cup unsalted butter, divided 113 grams (1 stick)
• 2 medium yellow onions finely sliced
• 4 pounds Yukon gold potatoes about 8-10 potatoes, 1.8 kg
• 2 teaspoons salt divided
• 1 cup heavy whipping cream 240 ml
• ½ teaspoon ground thyme
• 1 teaspoon garlic powder
• 1 cup shredded Gruyère 115 grams
• 1 teaspoon black pepper
• Fresh parsley for garnish optional

Instructions

• In a large skillet, melt 3 tablespoons of butter over medium heat. Add the sliced onions and stir so that the onions are lightly coated in the butter.
  
• Let cook for 25 minutes, stirring often.
  
• Then reduce the heat to medium-low and continue cooking until the onions are fully browned and jammy, about 45-55 more minutes. Once fully caramelized, remove them from the heat and set aside.
  
• Meanwhile, wash and peel the potatoes and cut them into 1-inch cubes. Add them to a large pot and fill the pot with water until the potatoes are covered. Stir in 1 teaspoon salt and place the pot over medium-high heat.
  
• Bring to a boil, and then reduce the heat to medium, cover, and let simmer for 10-15 minutes or until the potatoes are fork tender. Remove from the heat and drain.
  
• Use a potato masher to mash the potatoes until mostly smooth. Set aside.
  
• Melt 2 tablespoons of butter in a small saucepan over medium heat. Once melted, add the heavy whipping cream, ground thyme, and garlic powder. Bring to a simmer, stirring often. Remove from the heat and pour into the pot with the potatoes. Use the potato masher to combine the cream mixture with the potatoes.
  
• Once smooth, add in the Gruyère, the remaining 1 teaspoon salt, the black pepper, the remaining 3 tablespoons butter, and all but ½ cup of the caramelized onions.
  
• Stir the mashed potatoes until fully combined.
  
• Top the potatoes with the remaining caramelized onions and garnish with chopped parsley. Serve warm.
  

Notes

• You want your potato pieces to be roughly the same size so that they cook evenly.
• Mash the potatoes just until they are smooth. Overmashing can make the potatoes gluey instead of light and fluffy.

Photos of the step by step preparation process for French Onion Mashed Potatoes:

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