-bits Cake: Preheat oven to 190ºC . Line jelly roll pan with waxed paper; grease. Sift flour, cocoa, baking powder and salt together twice; set aside. Place eggs in small mixing bowl. Beat with electric mixer 5 minutes or until thick and lemon-colored. Slowly beat in sugar, a tablespoon at a time. Mixture will become very thick. Transfer to large mixing bowl. Beat in water and vanilla. Slowly add flour mixture; beat until smooth. Pour into prepared pan, spreading evenly to corners. Bake dozen to 15 minutes, or until cake tests done. Loosen from pan. Turn out on rack; remove waxed paper. Invert; cool completely. Combine baking chocolate, broken into pieces, and cream in heavy saucepan. Heat slowly; stirring constantly, until chocolate melts. Transfer to medium-sized mixing bowl. Stir in rum; chill 1 to 2 hours. Beat with electric mixer until stiff and thick. Cut cake in half crosswise. Place 1 piece of cake on small cookie sheet. Top with chocolate filling; spread to form even layer 1- half inches thick. Top with remaining cake layer. Chill at least 1 hour. Prepare frosting. Combine corn syrup, water and butter in small saucepan. Bring to boil; cook until butter melts. Remove from heat. Add chocolate bits; stir until chocolate melts. Cool at room temperature. Spread over top of cake. Chill until frosting sets. Cut cake into dozen squares; arrange on decorative plate.