In a large skillet or dutch oven, sauté onion, celery, and carrots over medium-low heat for 6-8 minutes, adding a little vegetable broth, as needed.
Meanwhile, using a separate pot, boil potatoes in water until potatoes are tender, about 10-15 minutes. Drain. Add the plant milk, garlic, pepper, and salt (if using). Adjust milk to desired consistency and adjust seasonings to taste. Set aside.
Back in the skillet, add the mushrooms; sauté 5-6 minutes.
Add garlic and peas; sauté 2-3 minutes.
Stir in flour, tomato paste, thyme, Worcestershire sauce, nutmeg, and wine (or vegetable broth); sauté 1-2 minutes.
Preheat oven to 375° F.
Stir in vegetable broth and red pepper flakes or cayenne; simmer for 10-15 minutes, stirring occasionally. Adjust seasonings to taste. Add additional broth, if needed.
Pour mushroom and vegetable filling into a large casserole dish.
Spoon and spread corn evenly over the top of the mushroom and vegetable filling.
Spoon and spread the mashed potatoes evenly over the top of the corn.
Bake for 25 minutes.***
Broil for about 5 minutes, until potatoes are golden and toasted, if desired.
Remove from oven and cool for 10-15 minutes.
Notes
• If you cook the veggies in a dutch oven on the stove, top it with corn and potatoes, and bake it in the dutch oven. Less dishes to clean. It’s a great dutch oven recipe when you’re camping.* I like using whole wheat flour, but you can use any flour - it's used as a thickening agent. If you follow a gluten-free diet, use a gluten-free baking blend. ** Lord Sandy’s makes a vegetarian Worcestershire sauce.*** If you don’t have an oven liner in place, be sure to place your shepherd’s pie on a baking sheet to catch any drips. Makes for easier clean up.