Heat the oven to 400 degrees.
Clean the potatoes and chop them into 1" slices. Bring a large pot of water to boil, and add the potatoes. Cook for about 20 minutes or until fork tender. Drain and set aside.
While the potatoes are cooking, rinse and drain the lentils. Place in a medium size pot, cover with 3 c. of water, and bring to a boil. Lower the heat, and simmer for about 20 minutes.
While the lentils and potatoes are cooking, dice the onion, garlic and shallot. Heat on medium for about 7 minutes.
Peel and dice the carrots, and dice the celery. Add to the onion mixture and cook for 5 minutes.
Slice the mushrooms and add to the onion mixture. Cook for an additional 5 minutes.
Stir in the lentils and the rosemary, heat through, and then remove from heat and scoop into your casserole dish.
Thinly slice the remaining 4 cloves of garlic and place the slices on top of the lentil mixture, evenly covering the top of the casserole.
Place the potatoes in a large bowl. Add the salt and almond milk, and mash well. Scoop the potatoes on top of the garlic layer, and press evenly over entire casserole.
Cover and cook for 35 minutes, until the edges of the potatoes are slightly crisp.