Cream together the butter and sugar in a large bowl.
Combine the self-raising flour and cocoa powder together in a separate bowl.
Mix the combined cocoa mixture into the creamed butter and sugar mixture.
The mix might look like it needs liquid, but keep working, using a spatula or your hands to form into a soft dough.
Add in the chocolate chips and mix gently to distribute evenly into the dough. Keep a few chocolate chips aside to sprinkle on the sliced cookies before baking.
Once the cookie dough is mixed. Split the dough into 3 portions and shape each into a roll about 6 inches (15cm) long. Do this on a floured surface with floured hands.
The length of the logs depends on how large you want your slice and bake cookies. Keep in mind that the longer the log, the smaller in diameter the cookies will turn out.
Wrap in plastic wrap and chill in the fridge for at least 30 minutes before slicing. See note 4
Remove the cookie rolls from the fridge. Use a sharp, knife, to slice the dough approximately ¼ inch (6mm) thick and arrange the cookies about 1 inch (2cm) apart on a baking tray lined with parchment/baking paper
Bake in a preheated oven of 340°F (170°C) for between 15 to 20 minutes
The baked cookies should feel firm on the top, not hard. Remove from the oven and transfer to cool on a wire rack before storing in an airtight container.