Melt the butter in a
high-sided saucepan and put the leeks in to brown, which have been
cut into round slices. When they start to brown, pour on top, little
by little, the cold milk. Mix in the peeled and sliced potatoes.
Season with salt and pepper and throw in the lumps of sugar. Bring it
to the boil slowly and let it simmer for about half an hour, then
take the liquid off the boil.
Pour the soup into
a tureen. Place on the top the slices of bread, toasted in oil and