Melt 1 tablespoon of butter in a large pan over medium-high heat. Add mushrooms; cook and stir 10 minutes. Remove and reserve.
Add the remaining 2 tablespoons of butter and your flour to the same pan to make a paste, which serves as the base to thicken our sauce. Cook the flour for about three - five minutes.
Add broth, wine, salt and pepper to pan. Whisk and stir until flour is dissolved. Continue stirring, bring to a boil, then simmer until thickened, 1 to 2 minutes.
Stir in reserved mushrooms. Pour into a gravy boat, and you're ready to serve.
Always use room temperature or cool wine and broth when adding to the hot roux. Gradually add and continuously whisk to separate the starches and thicken the gravy. Bringing the mixture to a low boil, enables the starches to thicken, about 2 minutes.
Keep Your Gravy Warm. Gravy thickens as it cools which creates a pudding like texture so you will want to keep it warm in a thermos or water bath until you're ready to serve.
How long will your gravy keep. Remember gravy is perishable. You can keep it in the fridge for 2 days.