Preheat your oven to 200C / 400F / Gas mark 6 and line a large baking sheet with baking parchment or use a silicone baking mat and place to one side.
In a large mixing bowl add in the flour, cocoa powder, baking powder, baking soda and salt and give a little mix to combine everything.
Rub the butter into the flour mix until it looks like fine breadcrumbs. Or use a food processor for quickness if you want.
Add in the sugar and chocolate chips and give a little stir to mix it all together.
Pour in the lightly beaten egg and gently stir to bring it all together. Add in the milk a little at a time, you just need enough to bring the mixture together. You don't want it to be a super sticky dough.
Scoop out the mixture into 10 equal sizes onto your baking sheet, the beauty of these rock cakes is they are not meant to be exact and perfect looking.
Sprinkle a little sugar on top if you like an extra little crunch and pop them in your hot oven for 15 to 20 minutes.
Check on them after 15 minutes, they should sound a little hollow if tapped on the bottom.
Transfer them to a wire rack to fully cool down.
These rock cakes freeze well for up to 2 months and kept in an airtight tin they will keep at room temperature for 5 days.