Soak the cashews overnight or for at least 4 hours.
Start by making the crust (or use store-bought): Make your ice water by adding your water to a glass with ice. Mix in the vinegar and set aside as you prepare the rest of the dough.
In a medium bowl, mix the flour and salt. Add the butter and cut into the flour using a pastry
cutter or fork. The butter should be the size of large peas.
Add 1 tablespoon of the cold water/vinegar to the flour mixture at a time. You should need 2-3 tablespoons. You don’t want the dough to be overly moist, but it should just hold together when pressed.
Place the dough onto a lightly floured surface. Lightly press the dough to form a rectangle using your hands or a rolling pin. Fold the dough, bringing 1/3 to the center, then the other. Flatten, then repeat this step 2 more times. This helps you get a flaky crust.
Keep the dough folded, wrap it up and let it cool in the fridge while you prepare the rest of
the recipe. You can also make the dough the day before and keep it in the fridge.
Preheat oven to 400F. Line a baking sheet with parchment paper. Prepare the filling: Heat olive oil in a large skillet over medium heat.
Add your mushrooms and leek and sauté until softened and fragrant, about 10 minutes. The liquid from the mushrooms should have evaporated.
Take the dough out of the fridge. On a lightly floured surface (I like to do this on the parchment paper), roll out the dough into a large rectangle or circle, about 1/4 inch thick.
Add the mushrooms and leek to the dough, keeping a 1 inch border around the edges. Fold the edges over the vegetables. Brush the dough with an egg wash (if not vegan) or plant-based milk.
Bake for 40 minutes or until the crust is crispy and lightly golden.
Meanwhile, place all the cashew cream sauce ingredients in a blender and blend until smooth.
Serve immediately with a drizzle of cashew cream sauce.