2 tablespoons butter
3 leeks, trimmed of roots and dark greens, cut crosswise into 1-inch pieces, and rinsed thoroughly
1 pound parsnips, trimmed, peeled, and cut crosswise into 1-inch pieces
2 apples, peeled, cored, and cut into 1-inch pieces
1 medium baking potato, peeled and cut into 1-inch pieces
1 can (14.5 ounces chicken broth
1/2 cup heavy cream
Heat the butter in a large pot over medium heat. Add the leeks and cook, stirring for 5 minutes. Remove about 1/4 cup for garnish and set aside.
Add the parsnips, apples, potato, broth, and 4 cup water. Bring to a boil; reduce heat and simmer, partially covered, until vegetables are tender, 20 to 25 minutes.
Working in batches, puree the soup in a blender until smooth. Return it to the pot; stir in the cream. Season with salt and pepper. Top with reserved leeks.