Use a baking tin (24 x 8 cm) and line with butter.
Scrape the seeds from the vanilla pod and mix with the butter and half of the Hermesetas Granulated. Whisk the eggs with the rest of the Hermesetas Granulated in a separate bowl until soft. Add the two mixtures together and mix well. Mix flour and baking powder, add to the first mixture and mix well. Mash the bananas with a fork and add them, along with the walnuts. Butter the baking tin, add the mixture and allow to bake for 45 minutes at 175°C.