Preheat your oven to 350°F (175°C) and grease and flour a 9x13 inch baking pan. In a large bowl, whisk together the melted butter and granulated sugar for the brownie layer.

Beat in the eggs one at a time, then stir in the vanilla extract. In a separate bowl, combine the flour, cocoa powder, and salt, then gradually add the dry ingredients to the wet ingredients, mixing until just combined. Spread this batter evenly into the prepared pan.

In a medium bowl, whisk together the flour, baking soda, and salt for the cookie layer. In a separate large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.

Beat in the large egg and vanilla extract, then gradually add the dry ingredients to the wet ingredients, mixing until just combined. Stir in the chocolate chips and evenly dollop spoonfuls of the cookie dough over the brownie batter in the pan.

Bake the brookies for 25-30 minutes, or until a toothpick inserted into the cookie layer comes out with moist crumbs. Avoid overbaking to keep them fudgy and chewy.

Let the brookies cool completely in the pan on a wire rack before cutting them into squares. This ensures they set properly and are easier to slice cleanly.

Serve the Halloween Brookies as is, or with a scoop of vanilla ice cream. Store any leftovers in an airtight container at room temperature for up to 3 days or in the refrigerator for up to a week.