In a saucepan over medium heat, melt the butter. When it begins to foam, add the onions, lemon zest, and ginger and saute until the onions are translucent, about 10 min. Add the lemon juice with sugar, salt and pepper; continue to saute for 2-3 min longer. Add the water, raise the heat to high, and bring to a boil. Cover, reduce the heat to medium, and simmer until the broth is golden and the onions have almost completely disintegrated, about 30 min. Remove from the heat and strain through a sieve into a clean container; discard the contents of the sieve. Working in batches if necessary, combine the strained stock and the potatoes in a blender or food processor and puree until smooth. Transfer the puree to a clean saucepan and bring to a gentle boil. Ladle into warmed soup bowls and garnish each serving with a little of the parsley. "Citrus" by Ethel and Georgeanne Brennan ISBN 0-8118-0602-2 pg 70