Preheat your oven to 350F (180C). Line a baking sheet with parchment paper, or lightly grease the pan.
Mix nutritional yeast, melted vegan butter, and soy sauce together in a large bowl. Open and drain the tofu (no need to press it), then use your fingers to break and crumble the tofu into the bowl. Stir the tofu crumbles well making sure all of the tofu is evenly coated in the seasoning mix.
Spread the tofu mixture evenly over the pan. Bake for 35 - 40 minutes, stopping to stir the tofu every now and then. Keep a close eye on it towards the end so that it doesn't burn. You want the tofu to be nice and browned. The smaller crumbles will be darker than the larger crumbles, and that's ok because it will provide a variety of texture.
To prepare the rest of the filling:
In the meantime, melt the vegan butter in a large skillet over medium-high heat and then add the onion and garlic, about 5 minutes. Sauté until the onion turns translucent and begins to brown. Stir in the chopped mushrooms and continue to sauté until the mushrooms reduce in size, darken in colour, and begin to get juicy, another 5 - 10 minutes. Turn off the heat.
Whisk ¾ cup of the cold vegetable broth and cornstarch together in a cup or bowl. Pour the vegetable broth mixture over the mushrooms and stir in the baked tofu crumbles, breadcrumbs, and all of the spices. If the mixture looks a bit dry add ¼ cup more vegetable broth as needed.
To assemble the pie:
Turn your oven up to 400F (200C).
Divide the pie dough into two, then roll out half of the pie dough on a floured surface. You can see more tips on how to do this in this post. Line a 9" pie plate with the rolled dough. Spoon the mushroom tofu filling into the pie crust and then pack it down firmly. Roll the remaining half of the dough and place ontop of the pie. Pinch the edges together to seal the pie then cut slits on top to allow steam to release. You can optionally use leftover pie dough to cut leaves or other shapes and decorate the pie. Brush the top of the pie with aquafaba or non-dairy milk.
Bake for about 40 minutes until the crust is golden, keeping an eye on it near the end so that it doesn't burn. Remove from the oven and let rest for 10 minutes before serving.
For gluten-free: use a gluten-free soy sauce or tamari, sub the breadcrumbs for gluten-free breadcrumbs, and use a gluten-free pie crust.For oil-free: for the tofu crumbles sub the oil for aquafaba or vegetable broth. When cooking the onions, do a water or broth sauté. Use an oil-free pie crust alternative.Aquafaba: is the liquid in a can of chickpeas or white beans and I find that brushing this on your pie crust gets the best golden colour, but if you don't have that on hand you can sub plant-based milk.Ground cloves: are traditional in tourtiere. That said, I generally prefer to make my pie without them so it is up to you if you want the traditional flavour or not.Make ahead: the entire pie can be made the day ahead of time and then baked fresh. To do this, allow the filling to cool completely before assembling the pie. Once assembled, cover with foil and chill in fridge for up to 24 hours. When ready to bake, follow the baking instructions in the recipe, bake from chilled.