Break off the woody ends of the asparagus (if using fresh). Slice off the tops--these will be used as a garnish. Cut the asparagus stalks into 1/2-inch slices. Set the chopped asparagus aside.

Melt the butter in a medium dutch oven over medium heat. Add the potatoes and the onion. Stir to coat with the butter and cook for about 5 minutes or until the onion is softened.

Add the stock and the sliced asparagus stalks. Bring to a boil, reduce heat and simmer for about 10 minutes or until potatoes are soft.

Using a stick (immersion) blender, puree the soup. If you don't have a sick blender, use a regular blender or food processor. If the asparagus is not young and tender, you may have to put the soup through a sieve to eliminate any woody parts that remain.

Add the cream and heat through. Add salt and pepper to taste.

For the garnish, blanch the asparagus tops in boiling water for 3 minutes.