Heat oven to 350 degrees. Grease and flour two 23 cm round cake pans. Sprinkle pecans evenly over bottom of both greased and floured pans. Lightly spoon flour into measuring cup; level off. In large bowl, combine all cake ingredients except egg whites and chocolate. Beat 1.5 minutes at medium speed. Add egg whites, beat 1.5 minutes. Carefully spoon quarter of batter into each nut-lined pan; sprinkle with grated chocolate. Spoon remaining batter over grated chocolate; spread carefully. Bake at 180ºC or 30 to 40 minutes until golden brown and top springs back when touched lightly in center. Cool 10 minutes; remove from pans. Cool completely. In small saucepan, combine half c sugar, unsweetened chocolate and quarter c water; cook over low heat until melted, stirring constantly until smooth. Remove from heat; cool. In small bowl, combine half c shortening and 1 t vanilla. Gradually add 2 c of the powdered sugar until well blended. Reserve one third c white frosting. To remaining frosting, add cooled chocolate, remaining quarter c powdered sugar and enough water for desired spreading consistency. To assemble cake, place one layer, nut side up on a serving plate. Spread top with about half c chocolate frosting. Top with remaining layer, nut side up. Frost sides and 1 cm around top edge of cake with remaining chocolate frosting. If necessary, thin reserved white frosting with enough water for desired piping consistency; pipe around edge of nuts on top of cake.