Preheat the oven to 400°F.
If you're not using a premade crust, roll out your dough and drape it into a 9-inch pie pan. Press it into the pan, trim the excess, and crimp the edges if desired. Use a fork to poke a few holes in the bottom and sides of the pie crust.
Line the inside of the crust with a sheet of foil or parchment paper, then fill it with pie weights, dried beans, or rice.
Place the crust into the oven and bake it for 20 minutes. Remove the pie weights and foil or parchment paper (careful, as everything will be hot), then bake the crust for 10 to 15 minutes longer, until the crust is lightly browned.
Place the crust on a cooling rack and let it cool while you make the filling.
Place the coconut milk, tofu, cornstarch, and salt into a blender and blend until smooth. Set this aside for now.
Melt the vegan butter in a medium pot over medium heat. Whisk in the brown sugar and water. Heat the mixture to a simmer, then reduce the heat and let it cook at a low simmer for about 4 minutes, whisking frequently.
Whisk the tofu mixture into the brown sugar mixture. Continue heating up the mixture until it almost comes back to a simmer, but avoid actually letting it bubble. It's ready when it reaches a thick, pudding-like consistency. Remove the pot from heat.
Whisk in the whiskey, if using, and the vanilla.
Transfer the mixture to the pie crust, smoothing out the top with a spatula.
Let the pie cool for about 20 minutes, then cover it and transfer it to the refrigerator. Chill until fully set, at least 4 hours.
Slice the pie and top each portion with vegan whipped topping. Serve.