Start by cutting the mushrooms in slices, then sauté the mushrooms in a skillet with some olive oil until fully softened, which usually takes around 10 minutes.
Add the onion to a nonstick frying pan and cook for 5 minutes, or until softened.
Meanwhile, in a small bowl mix together the sauce by stirring together the tamari, miso paste, apple cider vinegar, erythritol and water.
Add the mushrooms to the softened onions, stirring for a minute to reheat and brown.
Pour in the sauce and if using the cornstarch or arrowroot powder.
Cook, stirring for 2-3 minutes over a medium heat, until the glaze thickens.
Serve hot.
