Pour the stock into a saucepan, bring it to the boil, then reduce the heat to low and leave it gently simmering.
Heat extra virgin olive oil and a knob of butter in a heavy-based saucepan. Add the onion and celery to sweat on a medium heat until softened. Stir in the rice with a wooden spoon and coat each grain with the oil.
Add the wine and allow to evaporate, stirring all the time. Stir in the zucchini, asparagus and peas. Add a couple of ladles of hot stock and, stirring continuously, cook until the stock is absorbed.
Add more stock and repeat. Continue adding stock, cooking and stirring in this way for about 20 minutes, until the rice is cooked. It should be soft on the outside but al dente on the inside.
Remove from the heat and beat in the butter, Parmesan, and asparagus heads. Grate lemon zest and add finely chopped mint. Pour is one final ladle of stock. Leave to rest for one minute, then serve.
