• Pre-heat your oven to 200C/180C Fan/Gas Mark 6. Line an 8" Square Pan with greaseproof paper.
• In a small bowl, break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn't burn.
• In a large mixing bowl, whisk together melted butter and both sugars. With an electric/stand mixer, go for a solid 3-5minutes so it is totally combined. Add in the eggs and vanilla extract and combine again.
• Whisk in the melted dark chocolate. Then fold in the flour and cocoa powder. Finally, add the chopped white chocolate and fold together.
• Pour into the lined tin and bake 30 minutes. Remove and let cool before frosting.

For the Frosting

• Add the butter and a handful (6/7) blackberries to a large bowl. Beat with a whisk on high for a minute to combine everything.
• Add half the icing sugar, whisk on high. Then add the remaining half and whisk everything on high until fluffy. Add icing sugar as required to meet your desired consistency. Spread over the cooled brownies, top with more blackberries - slice and serve!