Preheat your oven to 175C.
Pop all the ingredients except the walnuts into a food processor and blend for a couple of minutes until a smooth and sticky batter forms.
Crumble the walnuts into the bowl and stir in.
Spoon the batter into a lined baking tin or mould and press down with a spoon to make sure it's all nice and even.
Place in the oven and bake for 25 minutes, then leave for another half an hour to cool (as the brownies will continue to cook after they are taken out the oven).
For the frosting, pop the ingredients into your blender and whizz for about two minutes, stopping every 30 seconds or so to scrape the mixture down the edges so it's all equally blended.
Spoon this on top of your bake then enjoy!
