Place the carrots, celery, half of the onions and water into a large saucepan
Finely slice the ends off the asparagus spears (about 3cm) and add to the saucepan
Bring the stock to a low simmer and cook for 45 minutes
Add the spinach and simmer for 2 minutes, then blend the stock with a stick blender until smooth
Keep on a low temperature while you start the risotto
Place the oil into a large heavy-based non-stick saucepan and heat over a medium temperature
Add the rest of the onion, lower the temperature and sauté until soft
Add the garlic and continue to cook until soft
Then add the rice and cook, stirring gently, until the rice is covered with oil and starts to go opaque
Pour in the wine and simmer until the wine is nearly all absorbed
Add one ladle of the stock, a pinch of salt and stir to combine
Cook on a low simmer until all of the stock is absorbed
Continue adding the remaining stock a ladle at a time, stirring each time you add some, until the rice is cooked and has just a little bite when tasted
When all of the liquid has been absorbed, turn off the heat and stir in the cheese, zest and butter