I have been making leek soup for many years in the same way as this soup, but I created this with some left over asparagus, quite by accident. My family did not really like it*, but the staff at school loved it! Go figure. I think this would be a really great soup course for a formal dinner.
What you need: Use all the leek except the toughest ends of leaves.
4 leeks, washed well, and sliced into 1/4 inch pieces; one bunch of asparagus, cut into 1/2 inch pieces; about 1 litre of water and several packets of chicken broth crystals, or 1 litre of chicken broth -from a box or home made; 1 medium potato; salt and pepper; 1/2 litre of whipping cream.
In a large soup pot bring broth, leeks asparagus and potato to a boil. Reduce heat and simmer until vegetables are tender. Add salt and pepper to taste. Process the soup in a blender in small batches, until it is all pureed. Add cream and heat until just hot, but do not boil. Serve immediately.
* Ben heard the word asparagus and decided before he tasted it that it would be awful.
Option for simple leek soup omit the asparagus, and use milk instead of the cream.