Preheat the oven to 190 degrees, sieve the flour and cocoa powder into a mixing bowl, add the sugar and chocolate chips. Then crack the egg into a separate bowl, add the milk and oil and beat quickly with a fork. Pour the beaten egg, milk and oil to the flour, cocoa powder, and sugar. Mix all the ingredients together, quickly and lightly. Spoon the mixture into 12 muffin cases. Bake them in the oven for 20-25 minutes until they are golden brown and springy to the touch. Put them on a wire rack to cool for 10 minutes then enjoy!