Preheat oven to 350f. In a large bowl, beat eggs, oil, sugar and vanilla until well blended. In a separate bowl, mix flour, cocoa and salt. Gradually beat into egg mixture. Stir in walnuts if desired.

Pour into a greased 13x9" baking pan. Bake for 30 minutes. Let cool.

For filling, mix butter and sugars until light and fluffy. Beat in milk and vanilla. Gradually beat in flour. Spread over brownies, and refrigerate until firm.

For glaze, in a microwave safe bowl, microwave to melt chocolate chips and shortening, then stir until smooth. Spread over filling, then sprinkle immediately with nuts, pressing them down slightly. Let stand until set.