Place potatoes in a large pot and cover with cold, salted water.
Bring to a boil and simmer until fork-tender, about 10-15 minutes.
Drain well and return to the hot pot with the heat turned off. Mash the potatoes until smooth, then stir in the soy milk, salt, and white pepper until creamy.
Cover and set aside. 2.
In a large Dutch oven or skillet, heat the olive oil over medium heat.
Add the onions and cook, stirring occasionally, until lightly browned, about 5 minutes.
Stir in the minced garlic and cook until fragrant, about 1 minute more. 3.
Add the carrots, mixed root vegetables, cabbage, thyme, and sage to the pot.
Stir to combine, then pour in the vegetable broth, Braggs Liquid Aminos, and black pepper.
Add the crumbled tempeh and stir everything together. 4.
Bring the mixture to a simmer, then cover and cook until the vegetables begin to soften, about 5 to 10 minutes. Uncover, increase the heat to medium-high, and simmer vigorously until most of the liquid has evaporated and the sauce has thickened, another 5 to 10 minutes. 5. Position an oven rack about six inches from the top heating element and turn on the broiler.
Transfer the vegetable and tempeh filling to a 10-inch pie plate or similar baking dish. 6. Carefully spread the mashed potatoes over the filling, covering it completely. Use a fork or knife to create a decorative pattern, like a diamond crosshatch, on the surface. 7.
Place the pie under the broiler and cook until the potato topping is lightly browned and golden, watching closely for 3 to 5 minutes to prevent burning.
Remove from the oven, sprinkle with fresh parsley, and serve warm.