Heat butter in a large pot over medium heat.

Add onions and cook until soft and translucent about 5 minutes. Do not brown.

Cut the tips off one bunch asparagus and set aside. (This will be used for garnish later)

Cut potatoes into ½ inch dice

Cook, stirring occasionally, until the onions begin to soften, about 3 to 4 minutes.

Add the garlic and cook until fragrant, about 30 seconds.

Add the broth, first batch of asparagus, potatoes, salt, and pepper.

Bring to a boil, then reduce heat and simmer until the vegetables are tender, 15 to 20 minutes.

Cook the second batch of asparagus tips in salted boiling water for a few minutes until tender crisp.

Place small batches of the vegetables into blender (or immersion blender) and puree until smooth.

Return to your pot, stir in lemon and optional parmigiana cheese and herbs.

Taste for additional seasoning.

Add the asparagus tips to bowls of soup as garnish.