Heat the oven to 180C/160C fan/gas 4. Butter and line a 900g loaf tin. Trim the ends of the bananas and discard. Roughly chop the bananas, peel and all. Place in a food processor or blender and blitz until smooth. Tip into a bowl and set aside.

Using an electric hand whisk or stand mixer, beat together the butter and sugar with a pinch of salt until light and creamy, around 4-5 mins. Beat in the eggs, one at a time, then add the vanilla, yogurt and banana. Mix in the flour, baking powder and bicarb until combined. Fold through the walnuts and gently spoon the batter into the prepared tin. Bake for 50-60 mins until a skewer inserted into the middle comes out clean. Transfer to a wire rack and leave to cool in the tin for 15 mins before removing from the tin and leaving to cool completely.

For the honey peanut butter, beat all the ingredients together using an electric hand whisk or stand mixer until creamy. Cut the cake into slices and spread over the butter. The butter and cake will keep in airtight containers for five days.