Saute a diced onion in 1 tablespoon of olive oil with a sprinkle of salt on low heat for about 3-4 minutes.
Add diced mushrooms, garlic, and herbs, then turn up the heat to medium. Saute until the mushrooms start to release their juices.
Add vegan beef crumbles (or protein of choice) and cook for 2-3 more minutes.
Add 4 cups of frozen mixed veggies and saute for about 5 more minutes until they are thawed.
Sprinkle with 2 tablespoons of flour and mix well.
Add 1 3/4 cups of vegetable broth, 2 tablespoons tomato paste, and 1 tablespoon soy sauce then stir well.
Cook until the mixture starts to bubble and thicken, then pour it into a large casserole dish.
Make the vegan mashed potatoes
Fill a large pot about 1/3 full of cold water.
Wash and peel your potatoes, then cut them into cubes about 1 square inch in size.
Place the potato cubes in the pot of cold water as soon as you cut them. (This will keep them from turning brown.)
Add salt to the cooking water and bring the potatoes to a boil.
Adjust the heat so that they stay at a rolling boil for about 15-20 minutes until the potatoes break easily when pierced with a fork.
Drain the cooking water and place the potatoes back into the pot. Immediately add 2 tbsp vegan butter, 3/4 cup plain plant milk, 1/2 tsp salt, and 1/2 tsp garlic powder to the hot potatoes.
Mash with a hand potato masher until the potatoes are fluffy.
Assemble and bake the shepherd's pie
Spread a thick layer of vegan mashed potatoes over top of the "meat" and veggie sauce, then drizzle with 2 tablespoons of melted butter (or brown butter sage sauce).
Bake at 350° F for 30 minutes. You can turn it to broil for the last 3-4 minutes to brown the top if you would like.
Garnish with fresh thyme for a pretty presentation. (optional)
Notes
Use a large casserole dish. Your cottage pie will bubble when cooking and may drip in your oven if your dish is not large enough.
You may want to place a cookie sheet under your casserole dish to catch any drips.
Make sure that you use enough liquid when making your mashed potatoes so that they are light and fluffy since they will dry out a little in the baking process.