This low-fat, non-dairy version of the traditional recipe for Shepherd's Pie is adapted from a recipe by Richard Gilbert as seen on Food Network.
In a medium pot, place the potatoes in cold, salted water and bring to a boil. Reduce the heat to a low boil until the potatoes are fork tender. (About 15 minutes)
Remove 1/2 cup of the water that the potatoes were boiled in and set aside.
Drain the potatoes and return to the pot.
Mash the potatoes with the 1/2 cup of water that was set aside and 2 tbsp of the margarine until smooth.
Season the potatoes with salt and pepper to taste and set them aside.
Brown the ground turkey in a large saucepan over medium-high heat.
Remove the turkey from the pan and drain any excess fat. Set the turkey aside.
Spray the bottom of the pan lightly with vegetable oil.
Return the pan to medium-high heat. Add the onion, carrot and celery. Sweat the vegetables for 5 minutes.
Add the mushrooms and frozen peas and saute for 5 additional minutes.
Return turkey to the pan and add tomato paste, red wine, thyme, marjoram and rosemary. Simmer for 1-2 minutes.
Add the brown gravy and simmer 1-2 more minutes.
Season to taste with salt and pepper.
Remove from heat and let cool.
Preheat oven to 400 degrees F (205 degrees C).
Layer the bottom of the casserole dish with the turkey mixture and top with mashed potatoes.
Make uneven peaks in the mashed potatoes with a fork.
Cut the remaining margarine into small cubes and sprinkle over mashed potatoes.
Bake for 30-40 minutes (until the mashed potatoes are golden brown)
Remove from oven and cool for 5 minutes before serving.