In a bowl, soften the butter and mix it with sugar until smooth.

Gradually add beaten egg in two portions and mix well.

Sift cake flour into the mixture and fold gently with a spatula.

Form the dough into a ball and wrap it to prevent drying.

Prepare the chocolate dough using the same method as the basic dough.

Shape the chocolate dough into 15g balls and the basic dough into 13g balls.

Roll the basic dough thinly between two layers of plastic wrap.

Place a chocolate dough ball in the center of the rolled basic dough.

Wrap the basic dough around the chocolate dough and flatten slightly.

Place the cookies on a baking tray with adequate spacing.

Bake in a preheated oven at 160°C for 10 minutes.

Mix cocoa powder with warm water to create a thick paste for decoration.

Use tools like cotton swabs or toothpicks to draw designs on the cookies.

Bake the decorated cookies in a preheated oven at 160°C for 3 minutes to set the designs.