Instructions:
Step 1
Prepare the chocolate cake according to the package instructions.
Step 2
Once baked, let it cool completely in the pan, then invert it onto a large serving tray or cutting board.
Step 3
Use a sharp knife or cake leveler to slice the cake horizontally in half. Set the top layer aside on a separate plate.
Step 4
To make the filling, in a medium saucepan, whisk together flour, milk, and salt over medium heat.
Step 5
Cook, stirring constantly, until thickened to a gravy-like consistency.
Step 6
Remove from heat, stir in vanilla extract, and let cool completely in the refrigerator.
Step 7
In a medium bowl, cream together shortening, butter, salt, and granulated sugar until light and fluffy.
Step 8
Once the flour-milk mixture has cooled, gradually add it to the creamed ingredients, beating for about 10 minutes until the filling is light and airy, resembling the texture of Twinkie filling.
Step 9
Spread the filling evenly over the bottom layer of the chocolate cake, leaving a quarter-inch border around the edges.
Step 10
Carefully place the top cake layer over the filling.
Step 11
Frost the entire cake with chocolate icing, ensuring a smooth finish.
Step 12
For best results, freeze the cake briefly to set the filling before adding additional layers of icing.
Serve and enjoy!