Sift plain flour, cocoa powder, baking powder, baking soda and salt together into a bowl, set aside.
Using a hand whisk to beat butter to smooth and fluffy. Pour icing sugar into it and mix well.
Add beaten egg in 3 batches and vanilla extract, mixing well after each addition until incorporated.
Pour in all the milk followed by the flour. Using a rubber spatula fold the mixture lightly till combined and smooth. Lastly add chocolate chips into it and mix well.
Divide chocolate mixture into cupcake liners to 3/4 full and bake in preheated oven at 180 deg C for about 30 mins.