Bake a Devil's Food cake in a well greased 9 x 13" pan. Let cool completely. Remove from pan and cut in half lengthwise. Remove top and set aside.
Place 4 tablespoons of flour and 1 cup of milk in a small saucepan. Cook on medium heat; stirring constantly until thick. Remove from heat and cool completely.
Beat for 15 minutes, 1 cup sugar, 1 cup crisco, 1/2 cup butter and 1 tablespoon vanilla. Add cooled flour mixture and beat another 5 minutes, scraping bowl several times and mixture is thick.
Spread over bottom half of cake. Replace cake top and refrigerate for 1 hour.
In saucepan add 4 oz. unsweetened chocolate squares, 1 stick of butter. Cook over low heat until chocolate is melted. Beat 1 egg and temper with chocolate mixture. Add egg mixture back into chocolate mixture, whisking until well combined. Remove from heat and add 1-1/2 cup of powdered sugar and 1 tablespoon vanilla. Beat until smooth, while still hot, pour over cake.