1) Melt the butter in a large pot over medium heat. Add the onions and garlic and cook until soft and translucent, about 5 - 10 minutes.

2) In the meantime, prepare the asparagus: snap off the blunt end and discard, then snap off the tips and set aside. The tips will be added to individual bowls as they are served. Cut the remaining spears into 1/2" pieces.

3) Add the chopped asparagus (except for the tips) to the pot, along with the broth, 1 teaspoon salt and 1 teaspoon pepper (adjust the seasoning later). Bring to a boil, then cover and turn the heat down to low. Simmer about 30 minutes until vegetables are very tender.

4) While soup is cooking, bring a small pot of salted water to a boil. Cook the reserved aspargus tips until tender-crisp, usually no more than 2 - 3 minutes. Drain and refresh under cool water or an ice bath to stop residual cooking. Set aside.

5) Puree the soup in small batches (so the blender doesn't overflow), then return the soup to the pot and bring back to a simmer. Stir in the lemon juice and grated Parmigiano-Reggiano (to taste). Taste and adjust seasoning with salt, lots of pepper, more lemon juice and Parmigiano-Reggiano if desired.

6) Ladle the soup into bowls then top each bowl with asparagus tips, fresh dill and, if deired, more Parmigiano-Reggiano and freshly ground black pepper.