Place the lentils into a medium saucepan and cover them with water. Place the pot over high heat and bring it to a boil. Lower the heat and let the lentils simmer until just a touch undercooked, about 20 minutes. Drain them in a fine mesh strainer when done.
While the lentils simmer, place the potato into a medium saucepan and cover it with cold water. Place the pot over high heat and bring the water to a boil, then lower the heat and let the potato simmer just until the pieces are easily pierced with a fork. Remove the pot from heat, drain the potato into a colander, then return it to the pot. Add 2 tablespoons of the butter and mash the potato with a potato masher, leaving some chunks.
Melt the remaining 2 tablespoons of butter in a large skillet over medium heat. Add the onion. Cook the onion for about 5 minutes, stirring occasionally, until it becomes soft and translucent.
Stir in the garlic, pecans, thyme, smoked paprika, rubbed sage, cinnamon, black pepper, cloves, allspice, and nutmeg. Cook the mixture for about 2 minutes, stirring constantly.
Gently stir in 3 cups of the cooked lentils (if you have some leftover, save them for another use), along with the soy sauce, and red wine vinegar. Cook the mixture for 2 to 3 minutes, stirring gently, just to reduce the liquid a bit. Remove the skillet from heat.
Fold in the mashed potatoes, then season the mixture with 1 teaspoon of salt, or to taste.
Drape one of your pie crusts into a 9-inch pie plate, gently pressing so it conforms to the inside of the plate. Trim any excess dough, then poke holes in the bottom and sides of the pie crust with a fork. Transfer the lentil mixture to the pie shell, gently packing it in. You may need to dome the top a bit.
Place your second crust over the filling, then trim any excess dough and pinch or crimp the edges to seal. Cut a few slits in the top of the pie and brush it with the non-dairy milk.
Place the assembled pie into the fridge and let it chill for 30 minutes.
Preheat the oven to 350°F. When the oven has fully heated up, place the pie inside and bake it for about 1 hour, until the top crust is golden brown.
Place the pie on a cooling rack and let it cool for at least 15 to 20 minutes before slicing. The longer it sits, the cleaner it will slice. I recommend shooting for 40 minutes — it will stay warm for a while.
Slice, serve, and enjoy!