Fry the onion in 50g butter with a pinch of salt over a moderate heat for 10 minutes until tender.
Add the rice, fry for 2 minutes more, then pour in the wine and simmer until absorbed.
Add the water a little at a time, waiting for it to be mostly absorbed between additions. Taste for seasoning all the time. About 5 minutes before the end (about 10 minutes after you started adding water), add the asparagus.
When the rice is still a touch too al dente for you, crumble in three-quarters of the gorgonzola (you can use or lose the rind as you like) and the remaining 25g butter. Stir until you are satisfied.
Serve with the hazelnuts and the remaining gorgonzola scattered on top.