from Wild Greens & Sardines
1 tablespoon unsalted butter
1 tablespoon olive oil
1½ cups sliced leeks
½ cup roughly chopped onion
¼ teaspoon kosher salt, plus more to taste
¼ teaspoon freshly grated nutmeg
1 teaspoon minced garlic
2 medium tart apples (such as Granny Smith), peeled, cored, and quartered
1 pounds celeriac, peeled and cubed
3-4 cups water
½ cup whole milk
Freshly ground pepper
For serving: piment d’espelette or smoked paprika
Heat the butter and olive oil together over medium heat in a large pot. Allow the butter to brown, just slightly. Add the chopped leeks and onion and cook, stirring often, until soft and shiny, about 5 minutes. Add the salt, nutmeg, and garlic and cook for another minute.
Add the celeriac, apples, and water to the pot. Cover and raise the heat to high. Bring the liquid to a boil, then reduce the heat to medium-low and cook, stirring occasionally, until the apples and celeriac fall apart, 30 to 40 minutes.
If you have an immersion blender, stick it into the pot and blend until smooth. Otherwise, transfer to an upright blender in batches and return to the pot. Add the milk, and taste to adjust salt and add pepper. Serve with a healthy dusting of piment d’espelette or smoked paprika.