Preheat the oven to 160 degrees C. Line a baking tin with a piece of foil or baking paper.
In a medium size microwave safe bowl heat the chopped butter and dark chocolate on high for 1 minute. Remove and stir until blended. You may need a further 30 seconds. Stir until smooth. Cool slightly so that you don't cook the eggs when you add them.
In another bowl, whisk the sugar with the eggs, using a whisk until light and creamy.
Add the melted chocolate to the whisked eggs, then add the vanilla and mix thoroughly with a wooden spoon.
Now sift in the flour and cocoa powder then mix well, you can now add the chopped up chocolates and mixed spice.
Using a spatula scrape the lovely chocolate mixture into the baking tin.
Put the tin in the oven and cook for 20-25 minutes, you can check the brownies by pushing in a cocktail stick or knife in the middle of the mix and when pulled out you should see some of the mix still sticking to the stick or knife. Just don’t overcook the mix or it becomes very dry.
Take the brownies out of the oven, and let the tin stand on a wire rack until it has cooled down. Once cool take the brownies out and cut into squares.