Preheat your oven to 400℉. Peel and cut the potatoes into 2 inch chunks. Place the potatoes into a pot and cover with water. Add a generous pinch of salt. Bring to a boil and cook for about 20 minutes or until cooked through.

While the potatoes are cooking, rinse and thinly slice the mushrooms, peel and dice the onion, peel and finely chop the garlic cloves, and finely dice the onion, carrot, and celery. Set aside. Wash and chop half of the parsley leaves and reserve the other half of remaining sprigs for garnish.

Place a sauté pan over medium high heat and add 1 tablespoon of vegetable oil into the pan. When the pan is very hot, add the Impossible Beef and break into pieces, allow to brown in the pan for about 2-3 minutes. Season with 1 ½ teaspoons Kosher salt and fresh pepper. Then stir the Impossible Beef with a flat spatula, scraping the bottom of the pan, and continue cooking and browning until little red is still showing, around 5 minutes. Remove from the pan and set aside on a dish.

Reduce the heat to medium, and add remaining 1 tablespoon oil, and the mushrooms, to the pan. Season the mushrooms with a pinch of Kosher salt and pepper, cook for about 2 minutes or until the mushrooms have released their liquid. Once the liquid reduces completely, add the onions, garlic, carrots, and celery and cook until soft, about 6-10 minutes. Add the soy sauce, vegetable stock and peas, and bring to a boil. Add the cooked Impossible Beef and the chopped parsley. Set aside.

Mash the cooked, hot potatoes in a mixing bowl with a masher, a hand mixer, a ricer, or a food mill. Heat the milk in a microwave for 30 seconds or in a pan on the stove top, add to the potatoes, and then add the butter and season with 2 teaspoons Kosher salt. Mix until fully incorporated. Season to taste and add additional salt and freshly ground black pepper if needed.

In a casserole dish, place the Impossible Beef mixture on the bottom and top with the mashed potatoes, spreading evenly. Bake in the preheated oven for 30 minutes. Remove from the oven, top with the crumbled potato chips and garnish with the reserved parsley sprigs. Serve while piping hot!