Dissolve yeast in warm water in a small bowl: set aside.
Cream shortening; gradually add sugar, beating well. Add eggs, one at a time, beating well after each addition. Add melted chocolate; beat well.
Combine flour and salt; add to creamed mixture alternately with milk, beginning and ending with flour mixture. Mix well after each addition. Stir in yeast mixture and vanilla. Cover and refrigerate overnight.
Dissolve soda in hot water; add to refrigerated batter, and stir until well combined.
Pour batter into 3 greased and floured 8-inch cake pans. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove layers from pans, and let cool completely.
Spread Chocolate Icing between layers and on top and sides of cooled cake.