Preheat an oven to 190 degrees Celsius/gas 5. Using an electric hand whisk, cream together the butter and sugar until it is pale. Sieve together the self raising flour and custard powder and slowly mix them into the creamed butter and sugar.

Using your hands, add the chocolate chips and the water. The heat of your hands will help to bring the dough together.Roll the dough into ping pong-size balls. Chill in the fridge for 10 minutes before baking.

To bake, arrange on two baking sheets lined with parchment paper (leave a good amount of space between the cookies, as they will spread during cooking).

Bake in the oven for 12-15 minutes, until risen and golden.

Once cooked, leave them to cool slightly before transferring them to a wire rack.