Mix together the ingredients as shown in Recipe ID: 1425955 "No Need for Chocolate! Cocoa Chocolate Mousse" to make the cream.
Slice the spongecake into a thickness of 1-1.5 cm. I used the chocolate spongecake from Recipe ID: 1428052
Place the sliced cake onto a sheet of parchment paper about the size of a sheet of printing paper. Thinly coat the surface with the cream and place a banana on top, as shown in the photo.
Completely cover the banana with the cream.
Since the cream is spread onto the banana, the sides will be somewhat lower.
Roll it up just like you would roll up a regular rollcake. Hold the edge of the paper closest to you and wrap it up away from you.
Place the seam end on the bottom and form the shape. (Don't smash it down too much, try to make it pretty high!)
Open up the paper and place the cake so that it's vertical from you. It'll be good if you eat it just like this too.
It will look like this when viewed from the side.
Close the openings on both edges of the roll cake by pushing it gently shut from the left and the right.
It will look like this from the above.
Thinly coat the surface with the cream.
Cut the cake in half straight through the middle.
Thinly slice the other banana into 2 mm slices.
Decorate the thinner ends of the cakes with the thin slices of banana to make the scales, and push them into the cream to stick. Don't stick bananas onto the thicker ends of the cake, leave those sides open.
Use the chocolate decorating pen to make eyes on the ends of the cake left undecorated.
If you look at the cakes from the cut end, it looks like their mouths are open.
Story Behind this Recipe
While making Recipe ID: 1426789 "For Children's Day! A Koinobori Cake That Kids Will Love" I felt like I wanted to try making it with chocolate and banana.
If the banana slices are too thick, they will probably be hard to use to decorate the cake! Since this cream becomes thick more readily than regular heavy cream, keep the whipped peaks on the softer side! For the times when it just seems like too much work to make, you can just use Yamazaki brand Rolled Banana Cake "Marugoto Banana." If you're worried about how easily the bananas change color, maybe you should use strawberries?