Preheat oven to 350°. Line bottom and sides of a 9-inch square pan with aluminum foil, allowing 2 to 3 inches to extend over sides; lightly grease foil.
Microwave chocolate and butter in a large microwave-safe bowl at HIGH 1 1/2 to 2 minutes or until melted and smooth, stirring at 30-second intervals. Whisk in sugar. Add eggs, 1 at a time, whisking just until blended after each addition. Gently stir in flour and next 4 ingredients. Pour mixture into prepared pan.
Bake at 350° for 44 to 48 minutes or until a wooden pick inserted in center comes out with a few moist crumbs. Cool completely on a wire rack (about 2 hours).
When brownies are cool make frosting. Beat cream cheese and butter at medium speed with an electric mixer until creamy. Gradually add powdered sugar and salt, beating until blended. Stir in vanilla.
Lift brownies from pan, using foil sides as handles; gently remove foil. Spread Cream Cheese Icing on top of brownies, and cut into 16-20 squares. Garnish, if desired.