Heat oven 425
In a large sauce pan brown 2 pounds IMPOSSIBLE Burger in 1 tablespoon olive oil over high heat
Remove meat from pan and set aside on a plate
Add 2 tablespoon butter to pan and sauté, carrots, onions, garlic, mushrooms, red pepper and celery for 8 minutes or until vegetables are just softened. Season with pinch of sea salt and black pepper
Make a roux. Heat 2 tablespoons butter in another small sauce pan over medium heat. Add ¼ cup flour and cook stirring constantly for 3-5 minutes. Turn off the heat and set aside
Add 2 cups chicken stock, sliced potatoes, and herbs to the cooked vegetable mixture. Simmer over medium heat for 20 minutes or until potatoes are tender. Add roux and stir until mixture is thickened.
Butter 2-9-inch baking dishes or a cast iron pan. Equally divide cooked IMPOSSIBLE Burger into the bottom of prepared baking dishes.
Spoon equal amounts of the thickened vegetable mixture over the IMPOSSIBLE Burger. Divided peas equally and sprinkle over vegetable layer. Pour ½ cup chicken stock into each pie dish for added moisture.
Cut puff pastry into ½ inch strips. Create a lattice over the pie by adding 5 strips of puff pastry about 1 inch apart on top of the pie filling, horizontally. Add 3-4 more strips vertically alternating pieces to create lattice by peeling back the 2nd and 4th strips first, then peel back 1st, 3rd, and 5th, strips and add another strip of pastry. Continue until lattice is complete.
In a small bowl whisk 1 egg and 2 tablespoons water for egg wash. Brush puff pastry with egg wash and bake at 425 degrees for 30-40 minutes or until pasty is golden brown.