In mixing bowl, combine sugar, flour. cocoa, and salt. Add oil, eggs, and vanilla; beat at medium speed for 3 minutes. Stir in walnuts if desired. Pour into greased 13X9 in. baking pan. Bake at 350 for 30 minutes. Cool completely. For filling, cream butter and sugars in mixing bowl. Add milk and vanilla: mix well. Beat in flour. Spread over brownies: chill until firm. For glaze, melt chocolate chips and shortening in a saucepan, stiring until smooth. Spread over filling. Immediately sprinkle with nuts, pressing down slightly.

yields 3 dozen