Saute onion and mushrooms in a large pan.
Add the rice and stir for a minute or so, until the rice starts turning opaque and smells a little toasted.
Add the white wine and the garlic.
Let simmer for a minute, then add the broth and white pepper.
Bring to a boil, then cover and let simmer until most of the liquid is gone, about 35 minutes.
Meanwhile, blend water and cashews in a blender until completely smooth.
Stir the cashew mixture into the rice, cover again, and let simmer until all the liquid is gone.
Stir in the Parmesan substitute.
Serve with additional Parmesan substitute to sprinkle on top, if desired.