Preheat oven to 350 degrees F and grease a 9x13-inch baking pan with non-stick cooking spray. Set aside.
In a large mixing bowl, gently whisk together the flour, cocoa powder, salt, and baking powder.
Add in sugar, chocolate milk, coffee, eggs and vanilla extract and whisk until fully combined.
Lastly, mix in the butter.
Pour cake mixture into the prepared pan.
Place the chocolate hazelnut spread into a piping bag or a sandwich bag and cut the tip off, draw lines down the top of the cake batter.
Drag lines in the opposite direction with a toothpick or knife to create a zigzag pattern on top of the cakes surface.
Bake for 35-40 minutes. The cake is done once a toothpick comes out clean from the center.
Remove the cake from the oven and let cool to room temperature.
While the cake cools, prepare the caramelized bananas. Slice the bananas into ¼-inch slices. Set aside. Melt the butter on a frying pan on medium heat.
Once melted, mix in the brown sugar just until combined.
Add in the bananas. Fold the bananas into the sugar mixture on medium heat for 4-5 minutes.
Serve warm over individual slices, sprinkle with chocolate shavings if desired.