Mix butter and sugar until becomes a pale yellow.

Add egg yolk and mix well. Add sieved flour and mix.

Separe 1/3 of the dough. Mixture the cocoa powder in the smaller portion.

Wrap both in plastic wrap and refrigerate for 30 minutes.

With your hands form the panda. Put in a tray covered with cooking sheet. Bake at 170°C for 20 min (10 min if you use a eletric oven)