1. Strain the pan juices into a measuring cup. Add enough broth to the pan juices to equal 3 cups.
2. Transfer the liquid to a medium size saucepan and bring to a boil, then reduce the heat to medium and continue to simmer.
3. Place another saucepan over medium heat, then add 2 T. of the butter. Allow to melt, then add the onions and sauté for two minutes, stirring frequently.
4. Remove the pan from the heat and add the vermouth. Return to the heat and reduce by half.
5. Add the remainder of the butter, and sprinkle the flour over the butter and onion mixture.
6. Whisk to incorporate, then add one cup of the hot broth to the roux, whisking vigorously to break up the flour. As the liquid incorporates add another cup of broth. Repeat the process until the gravy reaches the desired texture.
7. You may not need to add all of the portioned out broth. Continue to simmer over medium heat. As the broth evaporates the gravy will thicken. When the gravy reaches the desired texture, add the cream while whisking. Simmer for an additional 15 minutes over low heat to allow the gravy to set up.
8. Season with salt and pepper, and serve.