2 lbs asparagus, roughly chopped
1 onion, chopped
3 Tbsp butter
5-6 cups chicken stock
1/2 cup heavy cream
salt and pepper to taste
Cook onion in 2 Tbsp butter until soft. Add asparagus, salt, and pepper, then cook while stirring for five minutes. Add broth and simmer, covered, until asparagus is very tender- about 15-20 minutes.
Puree soup in batches in a blender until smooth, and return to pan. Stir in cream, and season with salt and pepper. Bring soup to a boil and whisk in remaining Tbsp of butter.