Potato-Leek Potage with Sage

Makes about 10 cups, serves 6-8.

The warm aroma of sage with its peppery hint of mint and camphor balances rich foods and enlivens humble ones. Ours comes directly from Sicily where the climate and soil conspire to produce exceptionally fragrant herbs, cultivated with care by siblings Maurizio and Katia on their family farm.

Sage is key to the allure of this humble potage or soup of potatoes, leeks, and celery root. The soup is filling, makes a big batch, and freezes well, providing comfort and ease for the cool days ahead. Garnish the soup simply with croutons (try our Everything Croutons recipe), a spoonful of yogurt, or a thick slice of sourdough toast brushed with olive oil and rubbed with garlic.

Use slightly waxy potatoes, such as Yukon Gold or Red Bliss. If you can get your hands on locally grown potatoes, leeks, and celery root you’ll be rewarded with exceptional flavor. Be sure to clean the leek well before chopping it (instructions at the end of the recipe).

2 pounds potatoes, peeled
1½ teaspoons salt, divided
2 tablespoons olive oil
2 tablespoons butter
1 large leek, chopped, white and tender green parts (about 2 cups)
½ cup diced celery root (or ¾ cup diced celery)
1 large clove garlic, chopped
½ teaspoon freshly ground black pepper
4–6 leaves Sicilian sage, crumbled
¼ teaspoon Sicilian thyme, crumbled
1 Sicilian bay leaf
4 cups low-sodium chicken or vegetable stock
1 tablespoon minced fresh parsley
1 teaspoon fresh lemon juice

Cut the potatoes into ¾-inch cubes, transfer them to a mixing bowl and add 4 cups warm water and 1¼ teaspoons of the salt. Stir once or twice to encourage the salt to dissolve. Set aside.

Put the oil and butter into a heavy-bottomed soup pot set over medium-high heat. When the butter has melted and the oil shimmers, add the leeks. Cook, stirring frequently, until the leeks are translucent, 3–5 minutes. Stir in the celery root and cook for a minute or two, before adding the garlic and the remaining ¼ teaspoon of salt. Reduce the heat to medium, continue to stir frequently, and cook until the celery root begins to become tender, 3–4 minutes.

Add the pepper, sage, and thyme to the vegetables and cook for about a minute to release their aromas. Add the bay leaf, potatoes (including the water they soaked in) and the chicken or vegetable stock to the pot. Stir once or twice. When liquids come to a boil, reduce the heat so that they are quietly simmering. Cook until the potatoes are completely tender but not falling apart, 15–20 minutes.

Fish the bay leaf out of the pot. Purée the soup right in the pot using an immersion blender — we like this soup quite smooth, but feel free to purée it only partially if you like chunky soup. (Alternatively, use a conventional blender to purée the soup in batches).    

Stir in the lemon juice and parsley. Taste for salt and pepper. Serve hot.

As with many soups, the flavor is even better the next day, but you may need to add another drop or two of lemon juice to brighten it after re-heating the soup.

Cleaning leeks  As they grow, leeks often trap grit between their layers and so must be carefully cleaned before cooking. To clean them easily, cut away the root end and peel off the outmost layer of leaves; cut the leek in half lengthwise.

 Hold one half of the leek under cold running water while ‘fanning’ the layers with your thumb. Rinse until you don’t see any grit. Repeat with the other half and pat both halves dry. Remember to wipe your cutting board before using it again — grit may have been left behind when trimming the leek.