Heat ghee or oil in a pan on medium heat then dice the onion and mince the garlic.
Add the diced onion to the pan and sauté for 3-4 minutes or until translucent.
Once the onions are translucent, add the minced garlic and sauté for 2 minutes.
Add the ground bison to the onions and garlic and brown for 8-10 minutes.
While the bison is cooking, dice the potatoes and add them to a pot with boiling water and let boil till tender (about 8 minutes).
To the bison, add the frozen peas and carrots and sauté for 2-3 minutes.
Next, add the tomato paste to the bison, stir well, and cook for 1 minute.
Add the coconut aminos, thyme, rosemary, salt, and pepper. Let cook on low while you finish the potatoes.
Preheat the oven to 400°F.
Drain the cooked potatoes and return them to the pot on the stove on low heat.
Add the ghee, dairy free milk, salt, and pepper to the potatoes and mash them using a fork, potato masher, handheld mixer, or immersion blender.
To an oiled cast iron skillet or 9x9 pan, add the bison mixture in an even layer then cover the bison with the mashed potatoes using a spoon or spatula to evenly spread the potatoes over the bison completely.
Bake at 400°F for 30 minutes. Optional- turn the oven to broil once the shepherd's pie is cooked and broil it for 5 minutes till the potatoes are golden brown. Make sure to keep an eye on it so it doesn't burn.