Preheat the oven to 180ºC with heat up and down (no air). Grease or line a rectangular mold about 22-24 cm long. If it is shorter, a taller cake will come out, but the cooking time can vary. Peel the bananas without wasting pulp and weighing about 300-340 g.
Mash in a bowl with a fork to leave a paste with some lumps, to give texture. Add the melted butter, the brown sugar and the yogurt, and beat until sugar dissolves. Add the eggs and vanilla, beat lightly and sift the flours, yeast and salt on top. If the whole wheat bran remains on the sieve, add it.
Throw in a couple of handfuls of knife-chopped peanuts and combine until everything is just right, with smooth movements and without stirring excessively. Take to the mold and spread a few more peanuts on top, adding more brown sugar if desired, or ground cinnamon.
Bake for about 45-50 minutes until when puncturing the center with a toothpick it does not come out wet. Wait about 10 minutes out of the oven before unmolding and let cool completely on a rack.