Mashed Potato Soup

When the potatoes are tender, they should give way easily to a fork—not crumble into the cooking water before you can drain them. That little window matters in mashed potato soup: russets need to be soft enough to mash smoothly, but the pot still has to hold together through a second round of cooking. I keep the potatoes separate from the broth until they’re mashed, which makes it much easier to control the finished texture.

This soup starts with a buttery onion-and-garlic base, then a quick flour-and-broth mixture gives the milk and potatoes something to cling to. Once everything comes together, the pot needs a gentle simmer rather than a hard boil. Sour cream stirred in at the end gives the soup a pleasant tang and a creamy finish, with enough body to feel like a meal in a bowl.

Why Mashing the Russets Separately Keeps This Soup Creamy

Potatoes can go from fluffy to gluey if they’re worked too aggressively. Russets are especially starchy, which is why they mash into a soft base so readily; that same starch can turn pasty if you beat it in a blender or food processor. I mash them in a bowl before they meet the liquid, stopping when they’re mostly smooth rather than trying to make them perfectly whipped.

That separate mash also gives you better control over the soup’s thickness. The flour-thickened broth is already smooth before the potatoes go in, so the mash loosens into the liquid instead of clumping around unmashed chunks. Small soft pieces are fine—they make the soup feel homemade—but a bowl of large potato lumps usually means the potatoes needed another minute of mashing before they went back into the pot.

Think of the potatoes as the body of the soup, not a garnish stirred in at the end. Once they’re incorporated, keep the heat gentle and stir often so the thick mixture warms evenly instead of catching on the bottom.

What Each Ingredient Brings to This Potato Soup

• Russet potatoes — Their high starch content gives the soup its thick, familiar mashed-potato texture. Choose firm potatoes without soft spots; the inexpensive bag is fine here, since peeling and simmering do most of the work. Yukon Golds can stand in, but the soup will be less fluffy and more buttery in texture.
• Unsalted butter, onion, and garlic — Butter softens the onion without adding extra salt, while the onion gives the broth a mellow savory base and garlic adds a sharper note. A basic yellow onion is exactly right; there’s no need for a specialty variety. Chop it finely so it softens throughout rather than leaving crisp pieces in the soup.
• All-purpose flour — Flour thickens the broth before the potatoes are added, helping the finished soup hold together. Keep it fresh and lump-free; a standard pantry bag works well. For a gluten-free version, use a cup-for-cup gluten-free flour blend in its place and cook it with the butter as described below.
• Low-sodium chicken broth — Low-sodium broth lets the potato water and finishing salt season the soup without making it too salty. A carton brand you already like is fine; the potatoes, onion, and dairy soften the broth’s sharper edges. Vegetable broth is the useful swap if you want a meat-free pot.
• Whole milk and sour cream — Whole milk gives the soup more body than a lower-fat milk, and sour cream brings tang that keeps the potato and butter from tasting heavy. Use fresh dairy, but the standard grocery-store versions work well. Two-percent milk can replace whole milk, though the soup will be a little less rich; plain full-fat sour cream gives the smoothest finish.

Building the Soup Without Lumps or a Scorched Bottom

Simmer the Potatoes Until Fork-Tender

Put the peeled, 1-inch potato pieces in a 6-quart pot, cover them with cold water by 1 inch, and add 1 tablespoon of kosher salt. Bring the water to a boil over high heat, then reduce the heat and simmer for 15–20 minutes. The potatoes are ready when a fork slides into a piece easily; if the center still feels firm, give them a little longer before draining.

Mash While the Pot Is Empty

Drain the potatoes well and transfer them to a large bowl. Mash until mostly smooth, leaving only small soft bits if you like a little texture. Don’t leave large chunks, because they won’t disappear once they’re stirred into the thickened soup. Set the potatoes aside while you build the base in the same pot.

Soften the Onion Before Adding Garlic

Melt the butter in the pot over medium heat, then add the finely chopped onion. Cook for 5–7 minutes, stirring occasionally, until it has softened; it should smell sweet and look translucent rather than browned. Add the minced garlic and cook for 30 seconds. Garlic burns quickly, so stir it through the butter and move straight to the flour.

Whisk the Broth Smooth, Then Warm the Potatoes Gently

Stir in the flour and cook for 1 minute, then gradually whisk in the chicken broth until there are no dry flour pockets. Bring the mixture to a simmer and cook for 2 minutes, stirring often, so the broth thickens. Whisk in the milk, mashed potatoes, black pepper, and remaining 1 teaspoon of kosher salt; simmer gently for 5–10 minutes, stirring frequently, until hot and creamy. Don’t let it boil, and stir the bottom of the pot so the thick soup doesn’t stick.

Three Practical Ways to Adapt Mashed Potato Soup

Questions That Come Up When Making Mashed Potato Soup

Mashed Potato Soup

Mashed potato soup combines tender russet potatoes with a buttery onion and garlic base, chicken broth, and whole milk. The potatoes are mashed before simmering into a hot, creamy soup finished with sour cream.

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Prep Time 15 minutes mins

Cook Time 35 minutes mins

Total Time 50 minutes mins

Servings: 6 servings

Course: Dinner

Cuisine: American

Calories: 370

Ingredients Method Notes

Ingredients

  

• 3 lb russet potatoes peeled and cut into 1-inch pieces
• 1 tbsp kosher salt divided
• 1 tsp kosher salt divided
• 4 tbsp unsalted butter
• 1 yellow onion medium, finely chopped
• 3 cloves garlic minced
• 0.25 cup all-purpose flour
• 4 cup low-sodium chicken broth
• 2 cup whole milk
• 0.5 tsp black pepper
• 0.5 cup sour cream

Method

 

1. Put the potatoes in a 6-quart pot and cover with cold water by 1 inch; add 1 tablespoon of the salt.
2. Bring to a boil over high heat, then reduce the heat and simmer for 15–20 minutes, until the potatoes are very tender when pierced with a fork.
3. Drain the potatoes and transfer them to a large bowl; mash until mostly smooth.
4. Melt the butter in the same pot over medium heat, add the onion, and cook for 5–7 minutes, stirring occasionally, until softened.
5. Add the garlic and cook for 30 seconds.
6. Stir in the flour and cook for 1 minute.
7. Gradually whisk in the chicken broth until smooth.
8. Bring to a simmer and cook for 2 minutes, stirring often.
9. Whisk in the milk, mashed potatoes, black pepper, and remaining 1 teaspoon salt.
10. Simmer gently for 5–10 minutes, stirring frequently, until hot and creamy; do not boil.
11. Remove the pot from the heat and stir in the sour cream until combined.

Notes

For the smoothest soup, mash the potatoes until mostly smooth before adding them to the broth. Refrigerate leftovers for up to 3 days; freezing is not recommended because the milk and sour cream can separate. For a vegetarian version, use vegetable broth instead of chicken broth.