In medium skillet, melt butter and saute onions and celery over low heat until tender. Add sorrel, chicken stock and water. Bring to boil and cook for 10 to 15 minutes.

Strain, reserving stock. Puree sorrel, celery and onions, adding stock until smooth. Add to remaining stock. Garnish with creme fraiche.

Creme fraiche: Mix 1 cup heavy cream with 1 cup sour cream until well blended. Cover well and refrigerate overnight.