Make Cookies: Preheat oven to 375°F. Cream butter and sugar. Add eggs, vanilla, and milk. In a separate bowl, whisk together flour, baking powder, baking soda, and salt. Add dry ingredients to wet and mix until just combined.

Chill and Bake: Wrap dough and refrigerate for at least 30 minutes. Roll out the dough to ¼-inch thickness, cut out circles, and place on a lined baking sheet. Bake for 8-12 minutes.

Make Icing: Whisk egg whites until foamy. Gradually add powdered sugar until stiff peaks form. Add water until a figure eight disappears in 8 seconds.

Decorate: Divide the icing, and color one portion black. Transfer to piping bags and decorate the cooled cookies to resemble Jack Skellington. Let the icing dry completely before serving.