For the soup
In a soup pot, melt the butter and sweat the onions, garlic and shallots until tender. Add the asparagus stems, stock, and zest. Simmer until the asparagus stems are tender. Puree the soup using a food processor, blender, or immersion blender. Strain the soup through a fine-mesh sieve to remove the asparagus fibers. Stir in the salt and the milk. Chill the soup. The soup is ready to serve once it is completely cooled.
For the garnish
Serve the cold soup and garnish with the whipped cream and the asparagus tips.