Potato-leek soup is a classic for good reason: It’s comforting, satisfying and so much more than the sum of its parts. For this version, I turned to a slow cooker for a truly hands-off preparation that can simmer away for hours, or until you’re ready to eat. Even better, there’s no need to sauté the aromatics (think: leeks, onions and garlic) in a skillet to start the soup; a tip I picked up from Julia Child's rendition in Mastering the Art of French Cooking calls for simply simmering the soup’s ingredients together until tender, then puréeing. Skipping the sautéing step not only streamlines prep, but it keeps the flavors of the leeks and potatoes in perfect balance. The final flourish of lemon zest — stirred into the hot soup right before serving — brightens and enlivens all the flavors.
Technique Tips Leeks often have a lot of hidden dirt between their leaves. To clean them, trim the dark green leaves (saving them for stock or another use) and discard the root. Cut the trimmed leak in half lengthwise, then slice into small pieces. Rinse thoroughly in a big bowl of cold water, sloshing the water to release the dirt. Lift the leeks into a colander with your hands, leaving the dirty water behind. Repeat this step a few times, if needed.
Start the soup with 6 cups of broth, resisting the temptation to add more at the beginning. Because of their tightly sealed lids, slow cookers require less liquid than stovetop recipes since there’s no evaporation. You can always add more broth at the end of the cooking process to thin the soup to your desired consistency.
Toppings Keep things simple with snipped chives, as I’ve done here, or feel free to play around! Crispy bacon, shredded cheddar cheese, grated Parmesan, garlicky croutons or fried, crispy leeks are all fair game.
In a slow cooker, combine potatoes, leeks, onions, garlic, butter, broth, 1 tsp salt, several big grinds of black pepper and bay leaves. (Note: the ingredients may not be fully submerged in broth; this is okay, they’ll cook down considerably.) Cook on low for 4 to 6 hours.2.
After the soup has cooked fully, discard bay leaves. Using an immersion blender, blend the soup until smooth. Or, working in batches, transfer to a stand blender and blend on low speed until smooth. Return the puréed soup to the slow cooker. Add the cream and stir to combine. Adjust seasoning with salt and pepper, and add more broth, if needed, to thin the soup to your desired consistency. Stir in half the lemon zest and add more to taste.3.
Divide into bowls and top with chives.