Pre-heat the oven to 180°C (350°F) and line or grease two 20cm (8") inch pans.
Sift the flour, cocoa, baking powder and baking soda into a large bowl.
Stir in the white and brown sugar.
In a separate bowl, whisk the milk, vanilla, oil and eggs until well combined.
Add the wet ingredients to the dry and fold together. Add the chopped chocolate.
Finally, slowly add the coffee or hot water (it should be recently boiled) and stir until everything comes together.
Don't over mix, there will still be a few lumps left in the batter (also note that the batter is supposed to be runny, so don't panic).
Divide between the two prepared pans as equally as you can and then bake for around 30-35 minutes in the lower part of the oven.
The cakes are ready when they bounce back when gently pushed on the top, and an inserted skewer comes out clean.
Remove from the oven and leave the cakes in the pans for around 15 minutes before turning out onto a wire rack to cool completely before decorating.