Melt the chocolate wafers according to package directions (typically in a double boiler or microwave in 30-second intervals, stirring between each). Pour the melted chocolate into silicone skull molds, filling them completely. Freeze for 3-5 minutes until set, then pop the skulls out of the molds. Repeat this process 1-2 more times to build up thicker, more durable skulls. Set the finished skulls aside in the freezer while you prepare the brownies—they'll stay perfectly firm.

Preheat your oven to 350°F and line a 9x13 inch baking pan with parchment paper, leaving a slight overhang for easy removal. Crush the chocolate sandwich cookies into roughly 1/4-inch pieces—you want some texture variation, not fine crumbs. Whisk together the flour, cocoa powder, and salt in a small bowl and set aside. This prep work ensures you're not scrambling mid-batter.

In a large mixing bowl, whisk together the melted and cooled butter with both the granulated sugar and brown sugar until well combined. Add the room-temperature eggs one at a time, whisking thoroughly after each addition to fully incorporate. Stir in the vanilla extract, red food coloring, and espresso powder, mixing until the batter is uniformly deep red and the espresso powder has dissolved—it won't add noticeable coffee flavor, but it deepens the red hue and enhances the chocolate notes. I like to use espresso powder here because it adds complexity without making the brownies taste like coffee.

Gently fold the dry ingredient mixture from Step 2 into the wet batter from Step 3 using a spatula, stirring just until no flour streaks remain—overmixing can lead to dense brownies. Pour the batter into your prepared pan and smooth the top. Bake at 350°F for 30-40 minutes; the brownies are done when a toothpick inserted into the center comes out with a few moist crumbs (not completely clean, as you want them fudgy). The baking time will vary slightly depending on your oven, so start checking at 30 minutes.

Remove the brownies from the oven and immediately sprinkle the chocolate skull chips evenly across the surface. Let them sit for 2 minutes to soften slightly, then spread them gently across the brownies with a spatula to create a thin chocolate layer. While the chocolate is still warm and slightly tacky, sprinkle the crushed cookies from Step 2 over the entire surface, pressing them gently so they adhere. This layering ensures the cookies stay in place and give you that signature texture contrast.

Let the brownies cool in the pan for 15 minutes, which allows the chocolate topping to set and makes them easier to cut. Once partially cooled, arrange the chocolate skulls from Step 1 on top of the brownies, pressing them gently into the chocolate layer so they stay put. Allow the brownies to cool completely to room temperature (about 1-2 hours), then lift them out using the parchment overhang and cut into 16 squares using a sharp, clean knife.