The night before making, cover the cashews in water and leave to soak. Alternatively you can boil the cashews over a medium/low heat for 5 minutes or until soft.
Once the cashews are soft, drain them of their soaking/boiling water and place them in the cup of a high-speed blender. Add the 150ml of water and blend on the highest speed until you have a very smooth cashew cream. It should be around the consistency of double cream.
In a mug, cover the dried mushrooms with boiling water and leave to soak for at least 2 minutes.
Boil the fusilli in liberally salted water until al dente. If the pasta is ready before the sauce, drain it but keep the pasta water. Toss the pasta in a little olive oil to stop it sticking together.
To make the sauce, heat the vegan butter in a skillet or frying pan over medium heat until melted. Add the onion and fry for a few minutes until turning translucent. Add the garlic and fry for a few minutes more. Do not allow the onions or garlic to brown.
Drain the mushrooms but reserve their soaking water. Chop the mushrooms very finely before adding to the frying pan and stirring well. Season with the salt and pepper.
Without stirring, remove around four tbsp of the mushroom soaking water. Mix it with the white wine and add to the frying pan. Reduce the heat to medium/low and allow the sauce to simmer until nicely reduced.
Add a large ladle of the reserved pasta water (around 200ml) and simmer again, stirring often, until reduced by about half.
Stir well before adding the cashew cream. Whisk to combine and allow to simmer one more time on a low heat until glossy and thick enough to coat pasta. Remove from the heat.
Dress the pasta with the sauce before serving and sprinkle with chopped parsley and a little extra black pepper if needed.