Creamy Potato Leek Soup With Croutons

A blender does the work here. A splash of cream at the end makes it restaurant-smooth, but you can leave it out. This potato leek soup is the bowl I crave the first cold evening of fall, when the light fades early and the kitchen windows fog up. It is silky, gently oniony and deeply comforting, and it is built almost entirely from pantry staples: potatoes, butter, broth and a few leeks from the market. Crunchy homemade croutons and a little fresh dill on top turn it into something special.

Prep 15 min · Cook 30 min · Serves 6

My grandmother made a version of this soup every October in her farmhouse kitchen in Vermont. Hers was chunky and peppery and served with thick slices of buttered bread. Over the years I have made it smoother and a little brighter, but the spirit is the same: simple ingredients, cooked slowly and served hot to people you love. It also happens to be vegetarian, inexpensive and easy to double for a crowd.

Getting to know leeks

Leeks are the quiet heroes of this recipe. They are related to onions and garlic, but their flavor is milder and sweeter, especially when cooked slowly in butter. You will use the white and light green parts. The dark green tops are tough, but do not throw them away; they are wonderful in homemade stock.

How to clean leeks

Leeks grow in sandy soil, and grit loves to hide between their layers. The easiest method is to trim off the root end and the dark tops, slice the leeks in half lengthwise, then cut them into thin half-moons. Drop the slices into a big bowl of cold water and swish them around with your hands. The sand sinks to the bottom while the leeks float. Lift them out with a slotted spoon or your hands, rather than pouring the water through a strainer, which would dump the grit right back on top.

Ingredients

• 3 leeks, cleaned and sliced
• 2 lb potatoes, peeled and diced
• 4 tablespoons butter
• 6 cups vegetable broth
• 1/2 cup cream
• Bread cubes for croutons
• Fresh dill

You will also want salt, black pepper and a couple of tablespoons of olive oil for the croutons. For the potatoes, Yukon Golds are my favorite. They are naturally buttery and blend into a velvety texture without turning gluey. Russets work too, but they make a slightly thicker, starchier soup. Day-old bread is ideal for croutons, since slightly stale cubes toast up crisp instead of soggy. A rustic country loaf or a sourdough is perfect.

How to make it

1. Soften the leeks in butter for 10 minutes without browning.
2. Add the potatoes and broth and simmer 20 minutes.
3. Blend until smooth and stir in the cream.
4. Toast the bread cubes in olive oil until golden and serve on top with dill.

Low and slow for the leeks

Melt the butter in a large pot over medium-low heat, then add the leeks with a good pinch of salt. The salt draws out moisture and helps them soften. Stir every minute or two. You want them limp, glossy and sweet, with no browning at all. Browned leeks taste more like caramelized onions, which is delicious but changes the character of the soup. If they start to color, turn the heat down and add a splash of broth.

Simmer until truly tender

Cut the potatoes into roughly even half-inch cubes so they cook at the same rate. After the broth goes in, bring it to a boil, then lower to a gentle simmer. The potatoes are done when a fork slides through a cube with no resistance at all, and a few pieces start to fall apart. Undercooked potatoes will leave little lumps no blender can fix.

Blending safely

An immersion blender is the easiest tool here, because you can blend right in the pot. If you are using a countertop blender, work in batches and never fill the jar more than halfway. Hot soup expands as it blends, and steam can push the lid off. Remove the small center cap from the lid and cover the opening with a folded kitchen towel to let steam escape safely. Start on low and increase the speed gradually.

The croutons make it

Homemade croutons are one of the easiest upgrades in any kitchen, and they take about ten minutes. Cut the bread into three-quarter-inch cubes. Warm a couple of tablespoons of olive oil in a large skillet over medium heat, add the bread and a pinch of salt and toss to coat. Let the cubes sit for a minute or two before stirring, so each side gets a chance to turn golden. Keep tossing until they are crisp all over.

For extra flavor, try one of these:

• Toss in a smashed garlic clove for the last two minutes, then discard it.
• Sprinkle with grated Parmesan right as they come off the heat.
• Add a pinch of smoked paprika for a little warmth and color.
• Use rye bread and a few caraway seeds for a deli-style twist.

Spoon the croutons on just before serving so they stay crunchy. A few torn sprigs of dill, a twist of black pepper and a thin drizzle of good olive oil finish the bowl.

Key takeaway: cook the leeks gently, simmer the potatoes until very soft and add the crunchy toppings at the last moment.

Storing and reheating

The soup keeps in a covered container in the fridge for up to four days. It thickens as it chills, so add a splash of broth or water when you reheat it gently on the stove. Store the croutons separately in an airtight jar at room temperature, where they will stay crisp for several days.

This recipe also makes a great freezer soup, with one important trick from our tester. Dairy can separate and turn grainy after freezing, so it is best to hold the cream back until you are ready to eat.

Freeze the soup before adding cream; stir it in when you reheat.

Recipe tester Molly Grant

Cool the soup completely, then pour it into freezer containers or zip-top bags laid flat, leaving a little room for it to expand. It keeps well for up to three months. Thaw overnight in the fridge, warm it slowly, then stir in the cream.

Make it your own

Once you have the basic soup down, there are many ways to change it up. Swap a third of the potatoes for cauliflower for a lighter bowl. Stir in a handful of shredded sharp cheddar at the end for a cheesy version. Top it with crumbled crispy bacon if you are not cooking for vegetarians, or with roasted chickpeas if you are. For a dairy-free soup, use olive oil in place of the butter and finish with a swirl of unsweetened oat milk instead of cream.

What to serve alongside

A bowl of this soup is filling on its own, but it shines as part of a cozy spread. We like it with a sharp green salad dressed with apple cider vinegar, a wedge of good cheddar and some sliced apples. Grilled cheese sandwiches cut into strips are a big hit with kids, who love dunking them. For a casual dinner party, serve small cups of soup as a first course, followed by a roast chicken or a simple pasta. A crisp white wine or a cold glass of apple cider pairs beautifully with the mild, buttery flavor of the leeks, and a plate of warm cookies is never a bad idea for dessert.

However you serve it, this is a soup that feels like a warm blanket. Use the servings scaler on the recipe card to make a big pot for a soup night with friends, and save a container in the freezer for the next chilly evening.