In a medium mixing bowl, whisk together the flour, cocoa powder, kosher salt, and baking soda until evenly combined.
Set the mixture aside while you prepare the wet ingredients.
Add the softened butter to the bowl of a stand mixer and beat until light and fluffy, about 2–3 minutes.
Add the granulated sugar and dark brown sugar and continue mixing for another 2–3 minutes.
Stop occasionally to scrape down the sides of the bowl so everything combines evenly.
Add the room-temperature egg and vanilla extract or vanilla paste.
Mix until everything is completely combined.
Slowly add the flour mixture to the wet ingredients.
Mix until just combined, being careful not to overmix the cookie dough.
The finished dough should be thick and fudgy.
Gently fold the coarsely chopped Halloween Oreos into the chocolate cookie dough.
Cover the dough and place it in the refrigerator for 30 minutes. While it's chilling, preheat your oven to 325°F.
Once the cookie dough has chilled, remove it from the refrigerator.
Scoop the dough into approximately 2-inch cookie dough balls.
Place additional chopped Halloween Oreos in a shallow bowl or plate. Gently press the top of each cookie dough ball into the Oreo pieces so they adhere to the dough.
Arrange the cookie dough balls on a prepared baking sheet, leaving enough room between each cookie for spreading.
Bake in the preheated 325°F oven for 10–12 minutes.
Once they're finished baking, allow the cookies to cool on the baking sheet for approximately 15 minutes before moving or enjoying them.
Store leftover Halloween Oreo cookies in an airtight container at room temperature for up to 3 days.
