Preheat oven to 175°C (347°F) with top and bottom heat
Mash bananas in a bowl, then whisk in eggs and vanilla sugar.
Add flour, protein powder, baking powder, salt, and cinnamon. Stir gently just until combined.
Pour into a pan lined with parchment paper.
Bake for 30 to 35 minutes until a toothpick comes out clean.
Cool in the pan for 10 minutes before lifting out.