1. Hydrate your chopped mushrooms with the boiling water. Cover and let sit for 10 minutes. Melt margarine in a small-medium saucepan over medium heat.
2. Sauté the onion lightly. Dont brown too much. Add the flour, and stir constantly with a wooden spoon until frothy. Do not let it burn! Add the mushrooms and their liquid and your vegetable broth.
3. Cook over medium heat to a boil, stirring constantly. After it comes to a boil, turn the heat down a bit and let thicken.