Preheat oven to 200C/180C Fan/Gas 6. Line a 8″ square baking tin with greaseproof paper.
Melt the dark chocolate by breaking up into small pieces in a bowl and heating for 30 second intervals in a microwave, stirring in between. Set aside to cool whilst making the brownies.
In a large bowl or the bowl of a stand mixer combine the melted butter, and both the brown and granulated sugars on a medium speed until totally combined.
Add the eggs and vanilla extract and mix again. Then check that the chocolate has cooled a little before adding in and combining. Add in the flour and cocoa powder and fold together. Finally add the chopped milk chocolate and fold in.
Pour into the tin. Bake for 30 minutes. Remove and let cool.
Once cool, make a thick icing with icing sugar and milk. Drizzle over the brownies and top with candy canes!