Combine unsweetened chocolate and butter in a small, heavy saucepan; cook over low heat, stirring constantly, until melted. Let stand 10 minutes. Beat eggs at medium speed of an electric mixer until thick and lemon colored; gradually add sugar, beating well. Add flour, salt, vanilla, and chocolate mixture; beat at low speed 1 minute. Spoon mixture into a lightly greased and floured 13x9x2 inch pan. Bake at 180ºC for 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool 10 minutes; spread Creme de Menthe Frosting (see below) over top. Chill at least 4 hours. Drizzle melted chocolate over frosting or pipe in desired design using metal tip No.3 or 4. Cut into bars immediately. Remove from pan, and chill at least 1 hour. Store in an airtight container in refrigerator. Yield 4 dozen. ----Creme de Menthe Frosting ----Combine all ingredients except walnuts in a mixing bowl; beat at high speed of an electric mixer until smooth. Stir in walnuts. Yield: enough for 4 dozen bars. From the Southern Living Cookbook