Preheat a large skillet over medium high heat, add onions and mushrooms. Use a little water if needed to prevent sticking. Stir frequently adding more water as needed, cook for 10-15 minutes until they have become soft and cooked all the way through.
Stir in garlic, thyme and rosemary or marjoram, stir and cook for another 1-2 minutes to release the natural oils in the spices.
Stir in the vegetable broth and bring it to a boil.
Meanwhile in a small dish mix together the Coconut Aminos, 3 T nutritional yeast, and cornstarch until a thick paste forms.
Add the paste to the skillet, using a whisk to blend it in, boil for about 1 minute, turn heat down to a simmer, stir constantly.
Add the balsamic vinegar and freshly ground black pepper, stir well.
Serve hot over mashed potatoes, rice or millet, green beans and lentil loaf.