Preheat oven to 160°Celsius. Grease and line a 6 inches square cake tin with parchment paper.
Melt butter over very low heat. While waiting for the butter to melt, chop chocolate into small pieces. Once butter has melted, turn off the heat and add the chopped chocolate. Stir until the chocolate has melted. Add brown sugar and whisk for about 30 – 45 seconds. Transfer the mixture to a large bowl.
Add egg to the butter-chocolate-sugar mix and whisk until the egg is all well incorporated, for about 1 minute. Add salt and stir.
Next, add vanilla essence and mix well. Sift flour and cocoa powder into the mixture and fold them in until well incorporated.
Finally, fold in the chocolate chips.
Pour the brownie batter into the prepared tin and level the top.
Bake for about 20 minutes at your normal cake baking temperature. Remove brownie from oven and let it cool in tin for about 10 minutes before transferring to a wire rack to cool completely.
Cut into 9 pieces or larger piece as desired and serve.