Preheat the oven to 425 degrees Fahrenheit
Make cashew cream by blitzing the raw cashews with ½ cup of vegetable stock or water. You can soak the cashews for 30 minutes if your blender is not a high-powered one. Set aside.
Heat the oil in a 10-inch cast-iron skillet or oven-safe skillet. Or, if you plan to make this in a baking dish use any skillet. Add the garlic, saute for a few seconds, then add the onions, celery and carrots.
Add a pinch of salt and ground black pepper to the skillet. Saute the onions, celery and carrots until the vegetables become translucent. Add the potatoes and mushrooms and saute for a couple of minutes.
Add the wine, if using, to the skillet (turn off heat or turn it down really low when you do this to avoid splashing any wine which could result in a fire). Cook the veggies, stirring frequently, until the wine has all but evaporated.
Add the herbs and the butternut squash to the skillet and stir-fry for a minute. Add the cashew cream and the remaining 2 cups of vegetable stock to the skillet and mix (add up to one more cup of vegetable stock for a saucier filling--I like mine saucy enough but not too saucy). Let it all come to a boil and simmer on a low flame for five more minutes or until the potatoes are tender. Stir in the sausage or tofu, if using, then add the parsley. Add more salt and ground black pepper as needed. Turn off the heat.
At this point, if you're planning to bake the pot pie in a baking dish, transfer the vegetable sauce carefully to the dish. If using an oven-safe skillet, you can continue to the next step.
Roll out the puff pastry to a size that'll cover the skillet, if that's what you plan to bake in, or of the baking dish you will use. Make 1-inch slits with a knife in the puff pastry, about an inch apart. This will give the juices an avenue to bubble and escape as the pot pie cooks.
Place the puff pastry carefully over the top of the sauce, making sure you cover it. Tuck in any excess pastry. You can brush on some oil on the surface of the puff pastry at this point for a more golden crust.
Place a sheet pan on a rack in the center of the oven. Place the skillet or baking dish on the sheet pan and bake 30-35 minutes or until the juices are bubbling and the puff pastry looks golden and crispy.
Serve hot or warm.