To make a quick broth, dissolve 1 bouillon cube (vegetable or mushroom) in hot water. In addition to being fat-free, this gravy is also gluten- and soy-free.
Combine the onion and the 2 tablespoons of broth in a small saucepan over medium heat and simmer until the onion is soft. Stir in the mushrooms and cook until slightly softened, then stir in the thyme, sage, and wine, if using. Add 1 cup of the remaining broth and bring to a boil. Reduce the heat and simmer for 5 minutes.