Position a rack in the center of the oven and preheat to 325F. Line an 8-inch square pan with aluminum foil and lightly butter the foil.
In a small saucepan over low heat, melt the butter. Remove from the heat and add the chocolate. Let stand for 5 minutes and then stir until smooth.
In a large bowl combine the eggs and salt; beat with a handheld electric mixer until frothy, about 30 seconds. Gradually beat in the sugar and continue to beat until light, 1 to 2 minutes. Add the vanilla and the melted chocolate and butter, beating until smooth. With a spoon, stir in the flour just until blended. Stir in the walnuts if you wish to use them and turn the batter into the prepared pan. Bake for about 30 - 35 minutes, until a toothpick inserted near the center emerges with a few crumbs clinging to it. Do not overbake or the brownies will be dry. Place the pan on a rack and cool to room temperature.
While the brownies are cooling, prepare the frosting which is optional, but a delicious addition. In a small heavy saucepan over very low heat, combine the cream and chocolate. Stirring constantly, heat just until melted and smooth. Remove from heat and stir in the confectioner's sugar.
With a knife, loosen the edge all around and pull out the cooled brownies by the aluminum foil and invert on a board. Peel off and discard foil. Return to brownies to the pan right side up and spread with fudge frosting. Let stand in a cool place for an hour or two. Cut into 16 small squares with a sharp knife.