Melt butter in a Dutch oven over medium-high heat. Add leeks, mushrooms, and salt; sauté 4 to 5 minutes or until leeks and mushrooms are tender. Add brandy, and cook, stirring often, 2 to 3 minutes.
Stir in gravy mix and remaining ingredients, and cook 3 to 4 minutes or until thoroughly heated and slightly thickened. Serve immediately.
* 2 tablespoons chicken broth may be substituted for brandy.
Note: Soup will thicken upon standing. To thin soup, stir in 1/3 to 1/2 cup milk or until desired consistency.