Bring a medium saucepan of water to a boil. Drop the kale into the water and simmer until kale is just-wilted and bright green, about 1-2 minutes. Using a slotted spoon, retrieve the kale and place it in a small bowl. Run some cold water over it before squeezing all of the excess moisture out. Set aside.
Drop the lentils into the saucepan of boiling water. Cook until lentils are tender, about 20 minutes. Drain and set aside.
Lightly wipe out the saucepan. Add the diced potatoes and one of the peeled garlic cloves to the saucepan. Cover the potatoes with cold water and place the saucepan on the stove over medium-high heat. Bring the potatoes to a boil and then simmer until very tender, about 18-20 minutes. Drain the potatoes.
In a large bowl, combine the drained potatoes, 2 tablespoons of the olive oil, 2 tablespoons of the non-dairy milk, and plenty of salt & pepper. Mash the potatoes with a masher until the potatoes have a mostly smooth texture and all ingredients are evenly mixed. Roughly chop the cooked kale and fold it into the potatoes. Set aside.
Preheat the oven to 375°F. Lightly grease a 9x13 glass baking dish with olive oil and set it on a baking sheet.
Heat the remaining olive oil in a large, heavy pot over medium heat. Add the onions to the pot and saute until slightly soft and translucent, about 3 minutes. Mince the remaining garlic cloves and add them to the pot along with the herbs. Stir until garlic is fragrant, about 30 seconds. Add the chopped mushrooms and stir. Place a tight-fitting lid on the pot and let it sit for 2 minutes.
After two minutes, remove the lid and season the mushrooms with pepper. Stir. Place the lid on and let the pot sit for another two minutes.
The mushrooms should have reduced in volume by at least a third at this point. Add the cooked lentils to the pot. Stir the mushroom and lentil mixture and then add the balsamic vinegar, tamari, and tomato paste to the pot. Stir and scrape up any browned bits at the bottom of the pot. Season the mushrooms liberally with salt at this point.
Add the vegetable stock to the pot and stir. Bring the mushrooms to a boil. In a small bowl, stir together the arrowroot powder and remaining 2 tablespoons of non-dairy milk to combine. Add the arrowroot slurry to the pot and stir. Let the mushrooms simmer until the surrounding liquid is slightly thickened, about 3 minutes.
Pour the mushrooms and gravy into the prepared glass baking dish. Dollop the mashed potatoes on top, and then gently spread them over the entire surface of the mushrooms with a spatula or the back of a spoon.
Drizzle the pie with olive oil and sprinkle with some black pepper. Carefully transfer the pie to the oven and bake until the filling is bubbling and the potatoes are lightly browned, about 25 minutes. Carefully remove the mushroom gravy pie from the oven and let it sit for a minute or two before serving.
To make this soy-free, use coconut aminos instead of the tamari soy sauce.
If you’re feeling it and your dish is deep enough, this pie can handle double the amount of potatoes.
You could use brown lentils in place of the French ones here. Alternatively, if you don’t have lentils on hand, you could use 1 ½ cups of whatever cooked pulse you like. White beans would be so good!
Corn starch substitutes perfectly for the arrowroot powder as our thickener here. -Use whatever mushrooms you like. I went for a mix of cremini, shiitake & portobello.
If you're using mixed dried herbs, go with half the amount specified (1 tablespoon).
If you don't have a glass baking dish, metal or Corningware is also fine for this mushroom gravy pie! As long as it's oven-safe and at least 2 inches deep.
Mushroom gravy pie with garlicky kale mashed potatoes is an ideal vegan, plant-based dinner option for your holiday table.