Prepare potatoes

1. Bring a large pot of water to a boil while you prepare your potatoes. Remove skins, and chop into chunks.
2. Once water is boiling, add potato chunks and cook until fork tender, about 8-10 minutes.
3. Strain and transfer potatoes into a large bowl, then mash until smooth using a potato masher or fork.
4. Add plant milk as needed to help then, and season lightly with salt and pepper. You want the potatoes to be smooth enough to spread.

Prepare filling

1. In a large saucepan over medium heat, sauté shallot, celery, garlic and fresh herbs in oil or vegetable broth until fragrant and tender. Add tomato paste, arrowroot starch, frozen vegetables, mushrooms and plant protein (if using) and sauté until evenly combined.
2. Add vegetable broth and simmer until the mixture thickens, about 3-5 minutes. Season with salt and pepper to taste.

Assembling the pie

1. Transfer filling into an oven safe baking dish or dutch oven and spread mashed potato mixture on top in an even layer.
2. Using a fork, gently score lines into the potato layer, then season with salt and pepper to taste.
3. Broil for 10-15 minutes until filling is bubbling and potato layer is lightly golden brown.