Mix the flour, baking powder, and salt in a bowl. Set the dry mix aside.
Beat the softened butter and granulated sugar until light and creamy. Add the egg yolk and vanilla extract, then beat until combined.
Stir the dry mix into the butter mixture until a soft dough forms. Wrap the dough and chill it for 30 minutes.
Heat the oven to 350°F and line a baking sheet with parchment paper. Roll the dough into short logs about 4 inches long, then pinch the ends to form bone shapes. Place them on the sheet.
Bake for 10 to 12 minutes until the edges turn lightly golden. Let the cookies cool completely on the sheet.
Whisk the powdered sugar, meringue powder, and water until the icing reaches a smooth piping consistency. Pipe thin lines along each cooled cookie to create the skeleton bone look.