Microwave the onions and leeks until tender or saute in water over medium heat until tender. Add stock and the asparagus and simmer until tender, about 15 minutes. Puree soup in blender in batches and strain through a fine strainer. Return to pot and season with white pepper to taste. You may now add the butter buds if you desire a butter flavor. Makes about 8 cups. Can be served hot or cold. Keeps well in the refrigerator for several days. I use this as my basic soup recipe and have successfully replaced the asparagus with beets, broccoli, carrot, acorn squash, butternut squash, and red kuri squash. You can make quite an impression by making both the acorn and butternut squash soups at the same time and serving them in the same bowl. Just slowly pour both soups into opposite sides of the bowl at the same time. I usually serve this with garlic croutons.