In a large sauté pan heat the oil over a medium heat. Place the mushrooms, salt, onion and garlic into the sauté pan and cook for 6-7 minutes, stirring often. Add in the brandy, and cook for 3-4 more minutes, there should be about a ¼ cup of liquid remaining in the pan.
Remove from heat and cool.
In a mixing bowl, combine seasonings, mustard, sour cream, mayonnaise and vinegar and blend well.
Fold in the mushroom mixture and green onions