Preheat the oven to 350°F and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, black cocoa powder, baking soda, and salt until evenly combined.
In a large bowl, beat the softened butter and sugar until light and creamy. Add the egg and vanilla extract and mix until smooth.
Gradually stir the dry ingredients into the butter mixture until a soft dough forms.
Lightly flour your work surface and roll the dough to about 1/4-inch thickness. Use a bat-shaped cookie cutter to cut out the cookies and place them on the prepared baking sheet.
Bake for 8 to 10 minutes until the edges are set. Let the cookies cool on the sheet for a few minutes before moving them to a wire rack.