Instructions:
- Prepare and bake the cake mix in a 9x13 inch pan according to package directions, adding the optional banana extract if desired.
- Remove the cake from the oven and let it cool in the pan for exactly 10 minutes.
- While the cake is still warm, use a long, thin wooden skewer or chopstick to poke holes all over the top, aiming to reach near the bottom. Make the holes about 1 inch apart.
- Slowly and evenly pour half of the can of sweetened condensed milk over the entire surface of the warm cake, allowing it to soak into the holes. Set aside.
- In a separate bowl, whisk the instant vanilla pudding mix with the cold milk for 2 minutes until thickened. Let it stand for 5 minutes.
- Spread the thickened pudding evenly over the cake layer. Drizzle the remaining half of the sweetened condensed milk over the pudding layer.
- Cover the cake pan tightly with plastic wrap and refrigerate for a minimum of 3 hours, or preferably overnight, to allow the liquids to fully absorb.
- Just before serving, beat the cold heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
- Gently spread the whipped cream over the chilled, set cake. Arrange the fresh banana slices artfully on top.
- Crush the vanilla wafers and sprinkle generously over the top. Place a few whole wafers around the edge for decoration. Serve immediately.