To make the asparagus stock, use the peels from the stems and the fibrous ends bits. I will say though if you are buying them from your chosen supermarket, they will already be trimmed down. Use vegetable stock or water. Just be aware, water will not give you the intense flavours. In this case double up on the quantity of asparagus in the recipe. Another alternative is to add baby marrows as I mention below. Not everyone has time to peel asparagus these days, but if you do you won't be disappointed.
Heat olive oil in a large sauce pan add finely chopped red onion fry for three minutes,
Add the smash garlic stir for 30 seconds
Add the Leeks, spring onion, and celery, and stir to coat with onion mix.
Add 1 cup of asparagus broth or vegetable broth to the pot, stir for 1 minute
Add the fresh asparagus and rosemary to the pot and another ladle of asparagus stock. Bring up the temperature put the lid on and steam for two minutes switch the pot off and let the asparagus continue to steam for 5 minutes
Add the cannellini beans and 500ml of stock bring to temperature check the seasoning
Using a stick blender, blitz the soup to a smooth consistency drizzle in the olive oil to thicken as necessary. Grate in the zest and a tiny squeeze of lemon if you like as on option.