Pre-heat the oven to 180/170 fan Celsius and line an 8 inch baking tin with parchment paper.
Mix the butter and sugar with an electric hand whisk (you can use a normal whisk or wooden spoon) and then add in the eggs. Beat the mixture until thick and fluffy.
Add in the melted chocolate and vanilla essence and mix in with the whisk.
Sift in the flour, sugar and baking powder and mix in with a spatula or wooden spoon until combined.
Mix in the chocolate chunks and then pour the mixture into the lined baking tin.
Place into a pre-heated oven for 31 mins. Once baked, allow the brownies to cool in the tin before serving.
Notes
* For the best results, once cooled. leave the brownies in the tin, cover them with cling film and leave them in the fridge overnight.