Mix butter and powdered sugar using a whisk until well combined. Use room-temperature butter for easier mixing.

Gradually add egg white in 2–3 portions, mixing thoroughly until the mixture becomes creamy.

Sift cake flour and coconut flour into the mixture and combine until no dry flour remains.

Fit a piping bag with a flat nozzle and pipe the batter into 7cm-long strips.

Bake in a preheated oven at 170°C for 10 minutes, then let the cookies cool completely.