Method (5 hours):
1) Blend all the ingredients, except the walnuts, banana and peanut butter, in a large bowl.
2) Place the dough out onto a floured surface and press it into a rough square.
3) Sprinkle the walnuts over the surface and roll up the dough.
4) Knead briefly again to ensure the walnuts are thoroughly distributed throughout the dough.
5) Shape the dough into a ball, place in a greased bowl and cover with a tea towel.
6) Let the dough rise in a warm place for about 3 hours.
7) When it has finished rising, divide it into 2 equal parts and roll each into a ball.
8) Place them on a baking sheet with enough space in between to allow them to double in size.
9) Sprinkle plain flour and leave them uncovered for 1 hour.
10) Preheat the oven to 240°C. Place the bread on the bottom rack of the oven and immediately drop the temperature to 200°C.
11) Bake for 40 minutes.
12) Allow the loaves to cool before serving. Cut two slices, spread over some peanut butter and top with a sliced banana.