1/2 c. butter
  8 lg. leeks, finely chopped (white
  4 c. (or more) chicken stock
  1/2 c. flour
  4 c. half & half cream
  1 1/2 lbs. Brie cheese, well chilled
     and cut into cubes
  Salt and pepper to taste
  2 tbsp. fresh chives, minced
     Melt 1/4 cup of the butter in a soup kettle over medium heat.
  Add leeks and saute until translucent, stirring frequently, about 4
  minutes.  Add stock and bring to a boil.  Reduce heat, cover, and
  simmer about 25 minutes.  Puree mixture in batches in blender.  Melt
  remaining butter in a saucepan over medium heat.  Add flour and stir
  2 minutes.  Blend in half & half; whisk until smooth. Add cheese in
  batches, stirring until cheese melts and mixture is smooth. Strain
  through fine sieve.  Return to saucepan.  Add leek puree and heat
  through.  Season with salt to taste.  Ladle into soup bowls and
  garnish with ground pepper and chives.  Serves 6.