Cake: Preheat oven to 350 degrees. In medium bowl cream shortening, sugar, eggs and vanilla until light and fluffy. Combine dry ingredients; add alternately with milk to creamed mixture. Pour batter into a well greased and floured 9-inch layer pan. Bake 30 to 35 minutes or until done. Cool 10 minutes; remove from pan. Cool completely. Filling: In a saucepan, combine sugar, cornstarch, milk and egg yolks. Cook and stir over medium heat until mixture boils. Boil and stir 1 minute. Remove from heat; blend in butter and vanilla. Cover and chill. Cut cake layer into two thin layers. Spread filling onto one cake layer; top with remaining layer. Glaze: In small saucepan combine water and butter. Bring to a full boil; remove from heat and immediately stir in cocoa. Beat in confectioners sugar and vanilla (whisk if necessary) until smooth; cool slightly. Pour onto top of cake, allowing some to drizzle down sides. Chill. Garnish with whipped cream or nuts if desired.