Preheat the oven to 200°C (400°F) (without fan).

Line a baking tray with baking paper.

Cream the butter and sugar until it is light and fluffy.

Add the flour, cocoa, baking powder, vanilla extract, and egg.

Beat everything together until the mixture forms into a soft dough.

Divide the mixture into 6 pieces.

Working with 2 or 3 pieces per baking tray, roll each piece into a log, and roll each log into a long, oval shape, with about 5 mm thickness.

Brush each piece with some egg wash, and sprinkle generously with pearl sugar.

Bake the cookies for about 10-12 minutes, taking care not to let the cookies brown too much.

While the cookies are still on the hot baking tray, cut them into 2 cm wide diagonal slices.

Leave the cookies to cool and firm on the tray for 5-10 minutes.