Preheat the oven to 340°F (170°C) for 15 minutes.

Soften 80g of butter at room temperature, then add 40g of sugar and a small spoonful of salt. Beat until soft. Add the egg in two parts, beating until well combined.

Add sifted cocoa powder and cake flour, and mix until there are no lumps. Then add chocolate chips.

Bake in the oven for about 15 minutes. Let cool before storing in an airtight container.