Place the lentils and 2 ½ cups vegetable broth in a small pot over medium-high heat. Bring the lentils to a boil and then reduce heat to a simmer, simmering the lentils for 15-20 minutes until cooked through and tender. Lentils should be soft but not mushy and most of the water will be gone. Once lentils are cooked drain any excess water and set aside.
Quarter the potatoes and place them into a large pot along with 8 cups of water. Add in 1 tablespoon of salt and bring to a boil. Allow potatoes to boil for 15 minutes or until potatoes are tender. Potatoes are done when they feel soft when poked with a fork. We leave the peels on the potatoes, but feel free to peel them if you prefer.
Preheat your oven to 425 F.
Meanwhile, in a large pan of medium-high heat add 1 tablespoon of olive oil for the Shepherd's Pie. Add in the chopped onions, carrots and celery and saute for about 5 minutes.
Next add in the mushrooms, garlic, rosemary and saute for 5 minutes longer. Add in the frozen corn and frozen peas and cook the mixture for 5 minutes until everything is heated through.
Mix the dried lentils into the vegetable mixture and stir in the soy sauce.
In a small bowl, whisk together the 2 tablespoons of vegetable broth along with 1 tablespoon of miso paste. Pour the miso mixture into the vegetable mixture. Stir the mixture until everything is nice and incorporated and remove from heat.
Once the potatoes are done drain them completely.
In the potato pot, pour in the almond milk and 2 tablespoons of butter. Using a masher, mash the potatoes until you have a smooth bowl of mashed potatoes.
Pour the vegetable and lentil mixture into a baking dish large enough to hold everything. Scoop the mashed potatoes on top and evenly spread out.
Place in the oven and bake for 25-30 minutes until the edges of the potatoes are starting to brown slightly.
Serve and enjoy!