In a small bowl, mix the flour with about 2 cups of vegetable broth until well dissolved. Once dissolved, add the remaining broth and mix. Set aside.
Preheat a 2 quart pot over medium heat. Saute the onion in oil for about 5 minutes, until translucent. Add mushrooms, garlic, thyme, sage, salt and pepper and saute for about 5 more minutes.
Add wine and turn heat up to bring to a boil. Let wine reduce for about 3 minutes. Add the broth/flour mix and the nutritional yeast, if using. Lower heat to medium and cook for about 20 minutes, stirring often.
Taste for salt and pepper and serve.