Lightly grease a 15 1/2 x 10 1/2 x 1 inch jellyroll pan and line the bottom with waxed paper; grease paper.
Preheat oven to 325°F.
Put shortening in a large bowl and beat with an electric mixer or large wooden spoon until fluffy, scraping side of bowl frequently.
Slowly add sugar, salt and vanilla to the shortening beating until mixture is smooth and no lumps remain.
Add eggs one at a time, beating well after each addition.
Mix buttermilk and baking soda in a small bowl (mixture will foam).
Alternately add flour and buttermilk-soda mixture to egg mixture in bowl, beating well after each addition, beginning and ending with flour.
Stir in melted chocolate and pour batter into prepared pan.
Bake 35 minutes. Turn cake out on a wire rack to cool and remove paper.
Pour evaporated milk, water and sugar into a small saucepan and cook, stirring frequently until sugar dissolves. Add fruit and bring to a boil, stirring constantly and cook until thick. Completely cool and stir in vanilla and chopped nuts.
In the top of a double boiler, melt chocolate pieces and butter over hot water. Remove from heat and stir in sour cream, vanilla and salt. Gradually beat in confectioners sugar until icing is of spreading consistency.
Flip cooled cake over and cut in half crosswise. Place one half on a serving platter and top with fruit-nut filling spreading evenly.
Place the remaining cake on top; frost top and sides with chocolate icing.