Melt the chocolate and butter together over hot water. Meanwhile, sift together 1 1/4 cups of the sugar, sifted flour, baking powder and salt. Stir the dry mixture into the chocolate mixture and blend. Stir in the milk and vanilla. Pour into a greased, square 9 by 9-inch cake pan. Mix brown sugar, remaining 1/4 cup sugar and cocoa powder and sprinkle over the batter. Pour coffee over and bake for 40 minutes. Serve warm or cold from the pan.