Large foil tray or a loaf tin lined with baking parchment
Preheat BBQ or oven to 180c.Melt the butter in a pan over a low heat, put to one side and allow to cool slightly. Add the sugar and beat until well combined. To save washing up you can make the whole thing in the pan.
Beat the eggs into the sugar and butter mixture, mix well.
Next add the mashed bananas and the vanilla.
Gently fold in the flour, baking powder and salt until the mixture is fully combined.
Finally add the chocolate and walnuts.
Pour the mixture into the prepared tray or tin.
Bake in the preheated oven or BBQ for about 30 minutes. Check after 20 minutes and turn the temperature down, or cover the cake if it is browning too quickly.
It is baked when it is golden brown on top and springs back when lightly pressed.