Begin by bringing a large pot of water to boil.
Peel and wash the potatoes. Cut in half and then into cubes. The total amount of potatoes should roughly measure between 6-7 cups. Once the water has boiled, add the potatoes and a generous dash of salt. Boil for roughly 20 minutes or until the potatoes are soft. Test by poking the potatoes with a fork. The fork should easily go through the potatoes.
While the potatoes are boiling, start making the mushroom gravy.
Wash the mushrooms and gently remove the stems by using a twisting motion with your fingers. They should remove easily. Once the stems are removed, slice the mushrooms rather thinly. Heat a cast-iron pan (or pan of choice) over medium heat. Add 1-2 tsp of oil to the pan. Once warm, add the sliced mushrooms. Let sauté for a few minutes, then add the chopped rosemary and thyme. Let sauté until the mushrooms are golden. Then add the balsamic vinegar, tamari, and miso paste. Stir to combine, let simmer for 1 minute.
After 1 minute, sprinkle the brown rice flour into the mixture and stir. Add the butter, the veggie broth and salt and pepper. Bring the gravy to a boil and then simmer for 5 minutes. Stir the gravy occasionally so it doesn't burn on the bottom. Gravy should thicken from the flour.
Once the potatoes are done boiling, drain the water and add the potatoes back into the pot. Use a potato masher to break down the potatoes, add the vegan butter. Mash thoroughly but avoid over mashing or you will produce a "gluey" consistency of the potatoes. Once mashed to your liking, add the chives and gently fold them in.
To serve, add the mashed potatoes to a plate and top with the mushroom gravy.
Best to enjoy immediately, but can store both the mashed potatoes and gravy in the fridge and reheat before enjoying again. The gravy will thicken from sitting in the fridge, so you may have to add a little more vegetable broth when reheating it.