Whip the butter using an electric mixer until fluffier and a little lighter in color.
Add in the sugar and whip together with the butter.
Add the egg yolk and vanilla into the butter mixture and mix until just combined.
Sift in your cake flour and fold into the butter mixture.
Weigh your dough and put half into a separate bowl.
Sift in the cocoa powder into one of the bowls and mix until fully combined.
Measure out the dough in to the ear, face, outer layer and extra pieces (ex: chocolate square piece between the rabbit ears, bear snout piece).
Roll out the dough and shape into the bear and rabbit shapes (freeze for a bit before putting the outer layer on to make this next process earlier).
Roll out the outer layer into a 12cm by 14cm rectangle and wrap around the cookies.
Let the cookies rest in the freezer for 30 minutes or the fridge of 1-2 hours.
When you are ready to bake your cookies, preheat your oven to 170C or 340F.
Slice your cookies into 12 - 13 cookies and lay onto a baking sheet lined with parchment paper (if you have a Silpat that is grid-like and allows the butter to fall through, it makes a crispier cookie compared to baking it on parchment paper!)
Place black sesame seeds onto the cookies to create your desired facial expressions using a toothpick and a little water.
Bake the cookies for 16-18 minutes before the cookies get too brown.
Transfer the cookies onto a cooling rack and let it cool to room temperature.
Itadakimas!