Mix softened butter with powdered sugar until creamy and fluffy. Add the egg and mix quickly to prevent separation.

Sift cake flour and cocoa powder into the mixture and combine using a spatula. If the dough doesn't come together, add milk gradually.

Wrap the dough in plastic wrap and refrigerate for 1 hour.

Roll out the dough to a thickness of 3–4mm using a rolling pin.

Cut out circular shapes using a smile cookie cutter and arrange them neatly on a baking tray.

Add facial features and press heart sprinkles into the dough for decoration.