Preheat oven to 415 degrees. Prepare or that vegan pie crust.
Bring a large pot of water to a boil. Add the potatoes. Par-boil for about five minutes, until tender. While the potatoes are boiling, add the cashews to a strainer and submerge them in the boiling water just enough so they heat up too - this will help soften them.
Warm a skillet over medium heat. Add the olive oil, onion and garlic. Saute for two minutes.
Add the shiitake mushrooms to the skillet. Saute for another 3 minutes. Turn heat to low and fold in the tofu, rosemary, sage, salt and pepper. Add the boiled potatoes over top, reserving one half cup of them for the creamy sauce.
In a blender: Add the boiled cashews, 1/2 cup of the potatoes, the nutritional yeast and the water or broth. Note: If using water add an extra pinch of salt here (or use tamari or soy sauce!) - do not add salt if using broth. Blend from low to high until silky smooth.
If your skillet is large enough, you can keep the ingredients in the skillet. If not, transfer all the skillet ingredients to a large soup pot. Pour the cashew sauce over top and gently toss everything together.
Fold in the parsley.
Lay the pie crust onto your pie dish. Pour int he filling and top with your top layer pie crust. NOTE: If using biscuit dough instead, you can skip the bottom layer of crust and dollop the biscuit dough on top! Traditional pie crust will look more elegant though, and slice more easily.
BAke at 415 for twenty minutes, then lower temperature to 350 to bake for another fifteen minutes.
Cool pie at least ten minutes before serving. Serve warm!