Mix butter,egg,sugar,flavor,in a bowl add the flour gradually then divide the dough in to two, add cocoa powder to one half and mix well,the other half should be plain.

Scoop the plain dough and deflate,scoop the dark dough and make a ball,place the ball at the center of the plain dough then cover evenly.

Use spoon to make the curve design just as it is in the picture.

Make another small ball with the dark dough.