Preheat oven to 350º. Grease 9 x 13 inch pan.
Cream the brown sugar and butter till light and fluffy. Slowly add flour and mix till blended. Pat into bottom of greased pan. Set aside.
Gently melt chocolate, butter (and espresso, if using) in microwave. Stir till smooth. Let cool slightly before adding sugar and vanilla. Then mix in eggs, one at a time. Stir in flour, and salt until just combined. Pour over crust.
Bake in middle of oven about 25-27 minutes. Remove from oven and immediately place in refrigerator.
Make glaze by gently heating chocolate, cream and butter in microwave till chocolate and butter are melted. Stir till smooth. Cool for about 10 minutes before spreading over brownies. Return to refrigerator. When chilled, cut into bars and serve.