Mix 50g of room-temperature unsalted butter with 70g sugar until smooth.

Beat 1 egg and gradually add it in three parts, mixing well each time.

Sift 100g all-purpose flour and 50g cocoa powder into the mixture.

Add a pinch of baking powder and salt, mix well, and refrigerate for 30 minutes to 1 hour.

Roll the dough into small balls.

Roll the balls in sugar and then coat them with powdered sugar.

Bake at 160°C for 10–15 minutes, turning occasionally.

Transfer cookies to a cooling rack and let them cool completely.