Irish Potato Leek Soup in a Slow Cooker

Irish-style potato leek soup is a simple, savory soup of potatoes, leeks, onion, and broth, finished here with cream and fresh chives. A slow cooker gently softens the vegetables while you get on with other things, and a quick blend at the end gives the soup a smooth, cozy texture.

Ingredients

3 medium leeks, about 1½ lb (675 g) before trimming, yielding about 4 cups (450 g) sliced and cleaned white and pale-green parts
2 lb (900 g) Yukon Gold potatoes, cut into roughly ½-inch (1.25 cm) cubes; peeling is optional
1 medium yellow onion, about 1 cup (150 g) chopped
2 garlic cloves, about 2 teaspoons (6 g) minced
2 tablespoons (28 g) unsalted butter
4 cups (946 ml) low-sodium vegetable broth or chicken broth
1 teaspoon (1 g) dried thyme
1 bay leaf
1¼ teaspoons (7.5 g) fine salt, plus more to taste
½ teaspoon (1 g) black pepper
½ cup (120 ml) heavy cream
1 tablespoon (15 ml) fresh lemon juice, optional
2 tablespoons (6 g) finely sliced fresh chives, for serving

Instructions

Clean and prepare the leeks. Trim away the root ends and the tough, dark-green tops, keeping the white and pale-green portions. Slice the leeks lengthwise, then cut them crosswise into thin half-moons. Put the slices in a large bowl of cold water and swish them apart with your fingers so grit falls to the bottom. Lift the leeks out rather than pouring the bowl through a strainer, and repeat if you still see sand. Drain well. Grit hides between leek layers, so take the time to rinse thoroughly.
Load the slow cooker. Add the cleaned leeks, potatoes, onion, garlic, butter, broth, thyme, bay leaf, salt, and pepper to a 5- to 6-quart slow cooker. Stir once to distribute the seasonings. The broth may not cover every piece of vegetable; the leeks and potatoes will soften and settle as they cook. Avoid adding extra liquid at this point, since too much broth can make the finished soup thin.
Cook until tender. Cover and cook on low for 6 hours, until a fork slides easily into the largest potato pieces. Slow cookers vary, so begin checking around the 5½-hour mark if yours runs hot or the potatoes are cut small. If you need a faster option, cook on high for about 3 to 4 hours and check for the same tenderness. Keep the lid on as much as possible; lifting it repeatedly lets heat escape and can extend the cooking time.
Remove the bay leaf and blend. Turn off the slow cooker and fish out the bay leaf. For a completely smooth soup, use an immersion blender directly in the crock, moving it around until no large pieces remain. Blend carefully to avoid splashing. For a more rustic bowl, pulse only part of the soup or mash some of the potatoes against the side with a potato masher. If using a countertop blender, work in small batches and follow its hot-liquid instructions; never fill it to the top with steaming soup.
Finish and adjust. Stir in the cream and lemon juice, if using. Taste before adding more salt, since broth brands vary in saltiness. If the soup is thicker than you like, stir in warm broth a little at a time until it reaches your preferred consistency. Serve promptly, topped with chives and extra black pepper. The listed 6 hours 5 minutes of cook time includes about 5 minutes for blending and finishing after the slow-cooker cycle.

Tips

Clean leeks carefully. Sand in the finished soup is the most common avoidable disappointment. Separate the slices in the water and lift them out, leaving the grit behind. If the leeks are especially dirty, rinse them in two changes of water.
Cut the potatoes evenly. Pieces close to ½ inch cook at a similar rate and blend smoothly. Larger chunks may need more time; very small pieces can break down early and make the soup unusually thick. Yukon Gold potatoes give a naturally creamy texture, while russets produce a softer, starchier result.
Choose the texture you want. An immersion blender is convenient, but it can make the soup gluey if you blend for a long time, especially with starchy potatoes. Blend just until smooth, or leave some chunks in place. For a lighter, less rich finish, use whole milk in place of cream, knowing the soup will be thinner and less velvety.
Season at the end, too. Broth and leeks differ in flavor, and slow cooking can soften the impression of salt. Taste after blending and add salt, pepper, or a little lemon juice gradually. Lemon should brighten the soup rather than make it taste distinctly sour.

Serving Suggestions

Serve the soup hot in bowls with chives and a few grinds of black pepper. Crusty bread, soda bread, or brown bread makes an easy accompaniment for dipping, while a simple green salad adds a crisp contrast to the soft, creamy soup. For a more substantial meal, offer the soup as a first course before roasted vegetables or a savory pie.

Set out optional toppings separately so everyone can finish a bowl to taste. A small spoonful of sour cream or plain yogurt adds tang, and crisp croutons bring crunch. If serving the soup as the main dish, include bread and one or two toppings rather than making the soup itself overly rich. Add chives just before serving so their fresh flavor and color remain noticeable.

Variations

Potato and leek soups have many home-style versions, and this recipe is an Irish-inspired take rather than a claim to one definitive traditional formula. For a more pronounced herb flavor, use 1 tablespoon (3 g) of chopped fresh thyme instead of dried thyme. You can also replace the thyme with 1 teaspoon (1 g) of dried marjoram, which gives a softer, slightly sweet herbal note.

For a dairy-free soup, leave out the butter and use 2 tablespoons (30 ml) olive oil. Replace the heavy cream with ½ cup (120 ml) unsweetened oat cream or a neutral, unsweetened plant-based cream. The result will be less buttery and may taste a little different depending on the substitute. Avoid sweetened or vanilla-flavored products. To keep the soup dairy-free, check that the broth and toppings also contain no dairy.

For a chunkier version, reserve about 1½ cups (350 ml) of the cooked vegetables before blending, then stir them back in with the cream. To add greens, stir in 2 packed cups (60 g) of thinly sliced spinach after blending and let the residual heat wilt it for a few minutes. You can also swap vegetable broth for chicken broth for a fuller savory flavor, or use extra vegetable broth if you want the soup to remain vegetarian.

Storage and Reheating

Cool leftovers in shallow containers and refrigerate them within 2 hours of cooking. The soup keeps for 3 to 4 days in the refrigerator. For the best texture, stir it before storing so the cream is evenly distributed. If you expect to freeze some, consider setting aside that portion before adding the cream; dairy can separate slightly after freezing, though the soup is still usable.

Freeze cooled soup in airtight, freezer-safe containers, leaving a little room at the top for expansion. For best quality, use it within 2 to 3 months. Thaw it overnight in the refrigerator, or reheat from frozen over low heat with a splash of broth, stirring as it loosens. Reheat only the portion you plan to serve on the stovetop or in the microwave, stirring regularly, until it reaches 165°F (74°C). If cream separates, whisk the soup gently as it warms; blending briefly can also help bring it back together. Do not leave cooked soup at room temperature for more than 2 hours.

Frequently Asked Questions

Do I have to peel the potatoes?
No. Yukon Gold skins are thin, and leaving them on saves time and adds a slightly more rustic look. Wash and scrub the potatoes well first. For a very smooth, pale soup, peel them before cutting; the flavor will be similar, but the texture and appearance will be more uniform.

Can I make this soup without cream?
Yes. The blended potatoes give the soup body, so you can omit the cream and serve it as a broth-based soup. For a creamy but dairy-free finish, use an unsweetened plant-based cream. Add any substitute near the end rather than cooking it for the full slow-cooker time, and taste again before serving.

Why is my potato leek soup too thick?
Potatoes release starch as they cook, and blending makes that starch noticeable. Stir in warm broth a few tablespoons at a time until the soup is the consistency you want. If it becomes too thin, leave the lid off and cook on high for a short time, stirring occasionally, or blend in a few more cooked potato pieces if you have them.

Can I put frozen potatoes or leeks in the slow cooker?
Fresh vegetables are preferable here because frozen potatoes can turn soft or grainy and release extra water. Frozen sliced leeks can work in a pinch, but thaw and drain them first; they may have a milder flavor and softer texture. Do not use frozen ingredients to extend the cooking time or assume they will cook at the same rate as fresh vegetables.

Can I prepare the ingredients the night before?
You can wash and slice the leeks, chop the onion, and cut the potatoes ahead, then refrigerate them in covered containers. Potatoes may brown when cut, so keep them submerged in cold water in the refrigerator and drain and dry them before adding them to the cooker. For food safety, do not leave cut vegetables or assembled soup on the counter overnight. Add the prepared ingredients and broth to the slow cooker shortly before starting it.

Can I cook the soup on high instead of low?
Yes. The high setting generally takes about 3 to 4 hours, depending on the slow cooker and the size of the potato pieces. Start checking near 3 hours; the vegetables are ready when the largest potato pieces are easily pierced with a fork. Use tenderness rather than the clock alone as your cue, then blend and finish the soup as directed.

More recipes to cook

Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

Spotted an error? Tell us and we will correct it (corrections policy).