Prepare the crepes batter. In a large bowl, combine the flour, eggs, milk and vanilla. Mix well, and let it rest for 10-15 minutes.
To make the hazelnut spread, blend the hazelnuts in a food processor. When well blended, add all other ingredients and blend well for about 5 minutes, until you have a smooth and slightly runny paste. (You might have to stop the blender every now and then to scrape off the sides). When ready, let it cool (it will become warm from the blending process) and transfer to an air tight container. It keeps in the fridge for up to two weeks.
Grease a frying pan and place on medium heat. When the pan is hot, add two tablespoons of batter and immediately swirl the spoon to form a crepe. After a few seconds flip the crepe on the other side and let it cook for a minute. You will have about 15 crepes, depending on the size you choose.
Assemble the pancakes:
Spread some hazelnut paste on the crepe. Add half a banana and roll tightly. Then cut the crepe in thick slices and serve!