Freeze the Tofu: Place the cake of tofu on a plate in the freezer, lightly covered with plastic wrap. Freeze until solid (a couple of hours).

Thaw the Tofu: Thaw the frozen tofu in the fridge for about 24 hours. The tofu will resemble a sponge.

Squeeze Out Excess Water: Gently squeeze the water out of the thawed tofu.

Shred the Tofu: Grate the tofu by hand or in a food processor until it resembles crumbles.

Sauté the Onions: In a large skillet, heat the vegetable oil over medium heat. Add the chopped onions, thyme, coriander, and black pepper. Sauté until the onions are translucent (about 5-7 minutes).

Combine Ingredients: Stir in the chopped walnuts and shredded tofu to the sautéed onions.

Season and Remove: Heat through. Stir in the lemon juice and tamari soy sauce. Taste and adjust seasoning as needed. Remove from heat.

Boil the Potatoes: Place the cubed potatoes in a saucepan and cover with lightly salted water.

Cook Until Tender: Bring to a boil, then reduce heat and simmer until the potatoes are soft and easily pierced with a fork (about 15-20 minutes).

Drain and Reserve Water: Drain the potatoes, saving 1 ½ cups of the hot potato water for the gravy.

Mash the Potatoes: Mash the potatoes with the butter and milk. Season with salt to taste. Aim for a creamy, smooth consistency.

Sauté the Mushrooms: Heat the vegetable oil in a skillet over medium heat. Add the sliced mushrooms, tamari soy sauce, and black pepper.

Cook Until Tender: Sauté, stirring occasionally, until the mushrooms are tender and have released their liquid (about 8-10 minutes).

Add Potato Water: Add 1 ½ cups of the reserved potato water and bring to a boil.

Thicken the Gravy: Slowly stir in the cornstarch mixture (cornstarch dissolved in cold water) and cook at a low boil, continuing to stir constantly, until the gravy is clear and thick (about 2-3 minutes).

Prepare the Dish: Oil a 9-inch square casserole dish or a 10-inch round cast iron skillet.

Layer the Ingredients: Layer the tofu mixture evenly on the bottom of the dish, followed by the mushroom gravy, and finally, top with the mashed potatoes.

Dot with Butter: Dot the top of the mashed potatoes with small pieces of butter (or margarine).

Bake: Bake in a preheated oven at 400°F (200°C) for 15-20 minutes, or until the top is golden brown and slightly bubbly.

Rest: Let the pie rest for 5-10 minutes before serving.