Special equipment: a pastry bag fitted with a large open star tip
For the frozen banana bites: Peel and slice the banana into 1-inch pieces. Heat up the chocolate and shortening for 30 seconds in the microwave in a bowl. Remove and stir. If any lumps remain, heat in 10-second increments until fully melted.
Place the banana pieces on a cookie sheet lined with parchment paper. Using two forks, place a banana piece on one fork and dip it into the chocolate. Make sure the banana piece is covered completely. Remove the banana piece from the chocolate and, using the other fork, gently move the banana piece onto the cookie sheet. When completed, place the chocolate-covered banana pieces in the freezer for at least 1 hour, preferably overnight.
For the chocolate cake: Preheat the oven to 350 degrees F. Prepare a 9-by-13-inch cake pan by rubbing with butter, sprinkling with flour and tapping out the extra.
In a large bowl, combine the flour, granulated sugar, cocoa, baking soda, baking powder and salt. Mix together with a wooden spoon, then set aside.
In a small bowl, combine the eggs, milk, oil and vanilla. Beat well with a hand mixer. Slowly add the boiling water and mix. Add the wet ingredients to the flour mixture, and fold and stir until smooth. Pour the batter into the prepared pan.
Bake until a cake tester inserted in the center of the cake comes out clean, 20 to 25 minutes. Remove the cake from the pan and cool on a rack.
For the whipped cream: Beat the cream and vanilla in a chilled nonreactive bowl with a whisk or an electric mixer just until the mixture holds a loose peak. (Lift the beater from the cream and look at the shape of the peak at the end of the whisk; it should hold a lazy curve.) Sift the confectioners' sugar over the cream and continue to beat just until it holds a soft peak. Take care not to overbeat the cream or it will be curdy. Refrigerate, covered, for up to 4 hours.
To assemble: When the cake is cool, cut in half with a long serrated knife. Place one half of the chocolate cake on a serving platter or cake stand. Cover the cake with strawberry pie filling (about 1 cup; you will have some left over, which can be refrigerated). Set the other half of the cake on top. Try to match up the ends that have been cut when stacking.
With a pastry bag fitted with a large open star decorating tip, pipe whipped cream mounds on top of the cake. Add sprinkles. Cut the frozen banana bites in half and set on top of the whipped cream. Serve immediately.
Be sure to time out your recipe. The fantastic frozen banana bites should be made ahead of time and properly chilled before you add them to the cake. You may also notice that I used a canned strawberry pie filling--this was very intentional! It really adds to the authentic banana-split flavor.