In a large skillet heat oil over medium high heat. Sautee mushrooms and onions until they are nicely browned (7 min). Add in garlic and stir until fragrant (about 30 sec)
Stir in the flour and cook for 1 minute. Whisk in the broth and scrape up all the browned bits from the bottom of the pan. Reduce to a simmer.
Simmer until thickened, then remove from heat. Taste for salt and pepper and season to taste.
