Preheat the oven to 180C.
Prepare the bread pan by coating it in butter and then sugar.
Beat the butter and sugar at #5 until it turns light.
Add eggs one at a time, until the mixture thickens.
Add the banana and blend in.
Add the yoghurt.
Add the flour and chopped walnuts and put the thermomix on reverse.
I added some milk to adjust to the right consistency (dropping consistency).
Pour everything into the bread pan and bake for about 45 minutes to 1 hour.
You'll need to rest the cake before cutting, or it will fall apart.