Add the vegetable broth, marsala wine and heavy cream, scraping up any browned bit. Simmer gently uncovered for 12-15 minutes, over med or medium-low heat, letting it thicken and reduce, deepen in color. It won’t be thick sauce- just thick enough to coat the back of a spoon. If you are having trouble reaching the right consistency, add some flour to help the sauce thicken up.