Ho Ho Cake

Directions

1. 1
   Grease a 10 1/2-by-14-by-2-inch pan and set aside.
2. 2
   Prepare cake mix as instructed on the box using the egg and oil.
3. 3
   Spread into reserved pan and bake in a preheated 350-degree oven for 20 minutes.
4. 4
   Remove from oven and place pan on a wire rack and let cake cool completely in the pan.
5. 5
   Prepare filling: Place flour in a small saucepan.
6. 6
   Slowly add milk, stirring until mixture is smooth.
7. 7
   Place pan over medium heat and cook, stirring constantly, until mixture is thick, about 10 minutes.
8. 8
   Place flour-mixture in a bowl, cover surface with plastic wrap and refrigerate until cool, about 2 hours.
9. 9
   In a bowl of an electric mixer, combine the cooled flour mixture, margarine, vegetable shortening and sugar.
10. 10
    Beat on high speed until light and fluffy, 7 to 8 minutes.
11. 11
    Spread evenly over top of cake and chill until filling is somewhat firm, about 2 hours.
12. 12
    Prepare icing: In a large bowl of an electric mixer, combine melted margarine, egg, melted chocolate, 2 1/2 tablespoons hot water and vanilla.
13. 13
    Beat on medium speed until blended.
14. 14
    Slowly add confectioners' sugar, beating until smooth.
15. 15
    Smooth icing over cake, taking care not to disturb the filling.
16. 16
    Chill until ready to serve.