Take butter and egg out to room temperature. Preheat the oven to 170°C and prepare a piping bag with a star nozzle.

Cream the butter using a whisk until it becomes smooth and fluffy.

Add powdered sugar and salt to the creamed butter and mix well.

Add the egg to the mixture and whisk until fully combined.

Sift cake flour and cocoa powder into the mixture and fold gently.

Mix the dough by cutting it in a straight line motion until it forms a single lump.

Transfer the dough into the prepared piping bag.

Pipe the dough onto a baking tray lined with parchment paper.