In a large mixing bowl cream together the sugar and shortening. Add to the creamed mixture the salt, vanilla and eggs. Combine the flour, cocoa and baking soda in another smaller bowl. Alternately add the dry ingredients and milk to the creamed ingredients beating well. Add the hot water and mix until the consistency of cake batter.
Bake at 350 degree in a prepared (greased and floured) 9×13 inch baking dish for 35 min or until a toothpick inserted in center comes out clean. Cool cake on rack.
For Frosting: In a saucepan over medium low heat combine sugar, cornstarch, water, semisweet chocolate squares, butter and vanilla. Stir continuously until mixture boils and thickens. This will resemble a thick chocolate pudding. Pour on cooled cake.