Cake: Preheat oven to 180ºC F. Grease 15.5 x 10.5 x 3 cm baking pan. Line with waxed paper. In bowl, cream butter, brown sugar, sugar, vanilla and salt. Add eggs, one at a time, beating well after each addition. Gradually add flour. Stir in 1 cup chocolate bits. Spread in prepared pan. bake 20-25 minutes. Cool completely. Loosen sides of cake. Invert onto floured cloth. Peel off waxed paper. Cut cake crosswise into 4 3- 0.75x10 inch sections. Spread 3 slightly rounded tablespoons frosting on one layer. Top with second layer. Repeat layers. Frost with remaining frosting. Frosting: Melt over hot (not boiling) water, 1 cup semi-sweet chocolate bits, stir until smooth. Set aside. In bowl, cream butter and confectioners' sugar. Add melted chocolate and vanilla; blend until smooth. Makes 1-10 inch cake.