Bake a Devil's Food Cake in a 9 x 13" pan. (You can line your pan with greased wax paper for easy removal.) Let cool completely. Remove from pan and cut in half lengthwise. Remove top and set aside. Put the bottom back into the pan.
Place 4 Tablespoons of flour and 1 c. of milk in a small saucepan. Cook on medium heat; stirring contantly until thick. Remove from heat and cool completely.
Beat for 15 minutes, 1 cup crisco, 1/2 cup butter and 1 tablespoon of vanilla. Add cooled flour mixture and beat another 5 minutes scraping bowl several times and mixture becomes thick. Spread over bottom of cake. Replace 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 and cook for 1 minute. Remove from heat and add 1-1/2 cups of powdered sugar and 1 tablespoon vanilla. Beat until smooth with whisk. Pour over cake