1. Place all of the ingredients in a pot, bring to a boil, then let them simmer for about 1/2 hour.
2. Remove from the heat, place in a bowl, cover, and place them in your refrigerator until cold. The longer you let them sit, the more flavor they'll have.
3. It's best to do this at least one day ahead.
4. If you want them to be more flavorful, remove the stems, or just cut them in half prior to simmering them. Exposing the inside of the mushrooms will permit more of the marinade to be absorbed.