Heat the oil and 50g/1¾oz of the butter in a large, heavy-based saucepan. Add the onion, celery, carrot and garlic and cook, stirring occasionally, over a low heat for 10 minutes, or until soft but not coloured.
Meanwhile, snap the woody ends from the asparagus spears and discard. Slice each spear on the diagonal into 4cm/1½in pieces. Pour the stock into a separate saucepan and bring to a simmer.
Add the rice to the softened vegetables and stir until coated in the butter and oil. Cook for a few minutes, then pour in the wine and keep stirring for 1–2 minutes, or until the liquid has evaporated.
Add the vegetable stock one ladleful at a time, stirring until all the liquid has been absorbed before adding more stock. Just before you finish using all of the stock, add the broad beans and petits pois to the rice and season with salt and pepper. At the same time, drop the asparagus into the remaining stock and simmer until al dente, then lift out using a slotted spoon and add to the rice.
Continue cooking until all of the stock has been absorbed and the rice grains are al dente. Take the pan off the heat and stir in 25g/1oz of the Parmesan and the remaining butter. Put the lid on the pan and leave for 5 minutes. Stir in the chopped herbs.
Spoon onto warmed serving plates and scatter over the remaining Parmesan. Serve immediately.