For the bat chocolate cookies, crumble the butter in the flour. Knead into a dough with the powdered sugar, egg yolks, melted cooking chocolate and rum. Let rest in the refrigerator for at least 1/2 hour.
Roll out the dough, cut out bats and place on a greased baking sheet. Bake over medium heat.
Warm the white chocolate coating and apply the eyes with a toothpick.