Preheat the oven to 200c/180c fan/gas mark 6
Sift the flour and cocoa powder into a mixing bowl and mix together with a wooden spoon.
Add the butter, sugar and eggs.
Use an electric hand whisk to mix until the mixture looks light and fluffy.
Stir in the chocolate chips.
Line a mini muffin tin with cases.
Fill each case half full with the mixture.
Bake on the middle shelf for 15 to 20 minutes.