Add cold diced butter and use a pastry cutter, fork, or your hands to mix everything together into a sand-like consistency. If using your hands, pinch the butter into the flour.
Add water 1 tablespoon at a time until the dough just comes together. Use your fingers to gently mix the dough as you add the water. You should be able to take a handful of dough and clump it together without it falling apart.
Gather the dough into a big ball. Cover and chill in the fridge for 1-2 hours.
Quiche
Preheat oven to 375°F/190°C.
Roll out the pie dough and press it into a 9-inch pie pan. Chill in the fridge for 30 minutes (if you're in a rush, you can place it in the freezer for 5-10 minutes, but don't leave it too long or the dough will get too cold and crack during baking).
Par-bake crust: Remove the pie pan from the fridge/freezer. Place a sheet of parchment paper on top and add pie weights or dried beans**1. Bake for 15 minutes, then remove the pie weights and parchment paper and bake for another 5 minutes or until golden on the edges. Set the crust aside while you prepare the filling. Reduce oven temperature to 350°F/180°C.
Sauté veggies: Heat olive oil in a skillet over medium heat. Add leeks and a pinch of salt and cook until leeks are soft, about 5 minutes. Add garlic, mushrooms, and zucchini and cook another 3 minutes or until veggies are tender. Remove from heat and drain off any excess water left in the pan. Set aside while you prepare the tofu filling.
Blend tofu filling: To a blender or food processor, add tofu, soy milk, nutritional yeast, paprika, herbs, salt, pepper, and turmeric. Blend until smooth. Add extra soy milk or water 1 tbsp at a time as needed to help blend. Pour into the pan with the veggies and mix to distribute.
Fill pie crust: Pour filling into crust and bake for 45-60 minutes until the filling is set and the top is firm. If the edges of the crust are browning too quickly, cover with a pie crust shield or aluminum foil.
Cool: Let the quiche cool for at least 10 minutes before cutting. Quiche can be served warm or cold. The filling will firm up more as it cools.
Notes
1) Par-bake crust: Pie weights/dried beans/sugar are usually recommended when par-baking pie crust to prevent the crust from shrinking. However, if you're feeling lazy you can just poke holes on the surface of the crust with a fork. To minimize crust shrinkage, make sure your crust is very cold immediately before baking. You may only need to bake the crust for 10-15 minutes, just until the edges are golden.