• Preheat oven to 350°F (177°C). Lightly grease an 8×8-inch metal pan with non-stick spray and line it with parchment paper (folded over the sides).
• In a medium saucepan or microwave-safe bowl, melt butter until fully liquid. Whisk in granulated sugar and brown sugar until glossy and thick.
• Whisk in egg, then vanilla. Whisk vigorously for 30-45 seconds until smooth and lighter in color.
• In a medium-sized bowl, whisk together flour, sifted cocoa powder, and salt. Gently fold dry ingredients into wet mixture until just combined.
• Fold in the chocolate chips until evenly distributed.
• Spread batter evenly in prepared pan. Bake 28-32 minutes until edges are set and a toothpick inserted 2 inches from edge has moist crumbs. Center should look slightly soft and glossy.
• Cool completely in pan for at least 1 hour.

Frosting

• Beat softened butter until creamy (about 30 seconds).
• Add powdered sugar, cocoa powder, vanilla, and salt. Mix on low until combined.
• Add milk 1 tablespoon at a time until smooth and spreadable (about 5 tablespoons total).

Assembly

• Using black writing icing, write "RIP" or spooky messages on Milano cookies.
• Spread a thin layer of chocolate frosting over cooled brownies.
• To cut brownies: Pull up on the parchment paper and transfer the brownies to a flat surface. Cut the brownies into rectangles. (I cut mine 4 x 3 to make 12 rectangular brownies). I found it easier to decorate them after they were cut.
• Sprinkle Oreo "dirt" over each frosted brownie rectangle, pressing gently.
• Press Milano tombstones into brownies about one-third down so they stand upright.
• Arrange candy pumpkins, gummy worms, and decorations around tombstones.