Trim leeks, and discard root end and green
tops. Cut remaining sections in half lengthwise, then wash thoroughly and
roughly chop into 1-inch (2.5-cm) pieces. Place leeks in a deep saucepan.
Add apple, stock and ginger. Bring to a boil over medium heat. Reduce
heat, cover and simmer until leeks are tender, 10-15 minutes. Remove from
heat and allow to cool slightly.
Pour mixture in a large bowl. Working in
batches, ladle into a food processor and process until it forms a smooth
puree, about 20 seconds. Transfer puree to a smaller saucepan. Place over
medium heat, add butter and stir until butter melts, about 2 minutes. Stir
in cream, salt and pepper to taste. Continue stirring over low heat until
heated through, about 1 minute.
