Heat oven to 350 degrees. Grease and flour two 9 inch 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 1/2 minutes at medium speed. Add egg whites, beat 1 1/2 minutes. Carefully spoon 1/4 of batter into each nut-lined pan; sprinkle with grated chocolate. Spoon remaining batter over grated chocolate; spread carefully. Bake at 350 degrees for 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 1/2 c sugar, unsweetened chocolate and 1/4 c water; cook over low heat until melted, stirring constantly until smooth. Remove from heat; cool. In small bowl, combine 1/2 c shortening and 1 t vanilla. Gradually add 2 c of the powdered sugar until well blended. Reserve 1/3 c white frosting. To remaining frosting, add cooled chocolate, remaining 1/4 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 1/2 c chocolate frosting. Top with remaining layer, nut side up. Frost sides and 1/2 inch 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.