Preheat the oven to Gas Mark 4 / 180ºc and line an 9x9" square tin with parchment paper.
Add the unsalted butter and white chocolate to a bowl and melt in short bursts in the microwave, stirring well each time, until smooth. (Ensure you stir well in between to stop it from splitting).
Once melted, stir in your caster sugar until combined.
Add in the mashed banana, eggs and golden syrup and stir again until combined.
Mix through the plain flour, and cornflour until you can no longer see any flour. Add in your milk chocolate chunks and chopped walnuts and stir until evenly distributed.
Pour the mixture into the lined tin and bake for 25-30 minutes (mine take 30 minutes), take them out the oven when there is an ever so slight wobble in the middle.
Let the blondies cool in the tin fully, and then set the blondies in the fridge for 3-4 hours or overnight for best results!
Once cooled, Slice your blondie into 9 slices and add a dollop of milk chocolate to the middle of the blondies, decorate with a full walnut and crushed up walnuts.
Refrigerate until the chocolate is set. Enjoy!
