Beat well butter with both types of sugar, add vanilla sugar too. Add melted chocolate and mix untill incorporated.
Add yolks and mix well.
In another bowl mix flour, cocoa and baking powder.
Move this mixture into the chocolate one and knead a dough.
Roll the dough into balls the size of large walnuts and place them on a baking sheet lined with baking paper. Press lightly on top. The distance between the cookies is about 3 cm.
Using the outside of a small measuring spoon, make an indentation in the middle of each cookie.
Bake cookies for 12 minutes.
Use a measuring spoon again to trace the center of the cookies if they have disappeared after baking.
Making Ganache
Pour the cream into a heavy-bottomed saucepan, add chopped chocolate, honey, butter and salt. Bring the mixture until smooth and transfer to piping bag.
Fill the center of each cookie with ganache.
Making Topping
Mix finely chopped chocolate with salt, transfer the mixture to a piping bag and place in a tall glass. Pour boiling water into a glass and wait until the chocolate is completely dissolved. Cool slightly. Cut the tip of the bag and decorate the cookies.