Preheat the oven to 200C/180C Fan/Gas 6. Line an 8 inch square tin. Melt the dark chocolate in the microwave in 20 second intervals. Set aside.
In a large bowl/the bowl of a stand mixer, combine the melted butter and both sugars. Add the eggs and mix again. Slowly incorporate the melted chocolate until everything is fully combined.
Fold in the flour and cocoa powder until just combined. Pour batter into lined tin and bake for 20 minutes.
Meanwhile, make the pecan pie topping by stirring together all ingredients. Once the brownies have had 20 minutes, remove from the oven, pour over the pecan topping and return to the oven for 15-20 minutes.
Once baked, remove from the oven and let cool on a wire rack before serving!