Preheat the oven to 350 degrees and line a baking sheet with parchment paper.
Stir together the flour, baking soda, and salt in a medium bowl.
In a large bowl, beat the softened butter with the brown sugar and granulated sugar until light and creamy.
Mix in the egg and vanilla extract until fully combined.
Add the dry ingredients to the wet mixture and stir until a dough forms.
Fold in the chocolate chunks evenly.
Roll the dough to about 1/4 inch thick on a lightly floured surface. Cut out shapes with a skull cookie cutter and place them on the prepared baking sheet.
Bake for 10 to 12 minutes until the edges turn golden. Cool on the sheet for a few minutes before moving to a wire rack.