Prepare the dough by adding the flour, salt, and sugar into a food processor. Pulse a few times to mix. Then add in the cold, cubed vegan butter. Pulse again to form crumbles. Finally, put the food processor on and stream in the cold water. Let it mix for 30 seconds to 1 minute until it forms a dough.
On a clean surface empty the dough out and knead with your hands. Knead for about 1-2 minutes until the dough comes together. Cut the dough into two even pieces and chill in the fridge for 30 minutes.
Meanwhile, add the vegan butter, onions, and garlic to a big pan. Cook for 5-7 minutes on medium heat until onions are clear. Then add in the mixed frozen veggies and tofu. Cook for 5 to 7 minutes until veggies are no longer raw on medium heat. Sprinkle the flour over the vegetables. Mix to coat.
Then add in the non-dairy milk, vegetable broth, and seasonings. Cook for 10 to 15 minutes over medium heat until thickened. Taste the filling and adjust any seasonings to preference.
Preheat the oven to 425°F (218°C).
On a clean surface roll the dough balls out to be about ¼ inch thick and 10 to 12 inches around. Only work one piece of dough at a time as it is very important for the dough to stay chilled.
Drape the dough over a greased pie dish and then press it in. Cut off any excess dough. Add the filling into the middle. Using the other piece of dough, roll it out again and drape it over the top. Cut off any excess dough.
Make an X on top to ventilate the pie. Then seal the edges by either fluting the pie or using a fork to press down on the edges.
Optional combine the non-dairy milk + a pinch of turmeric together. Brush on top of the pie to make it extra golden.
Bake for 30-35 minutes until it is golden brown on top. Allow the pie to sit for 15 minutes before enjoying. I like to spray mine with spray oil right before serving for a beautiful shine.