Preheat your oven to 350°F (175°C). In a large mixing bowl, beat together melted butter, brown sugar, and granulated sugar until light and creamy.

Add eggs one at a time and include vanilla extract, mixing until combined.

In a separate bowl, sift together all-purpose flour, cocoa powder, baking powder, baking soda, and salt. Gradually mix into wet ingredients and fold in Oreo crumbs.

Allow the cookie dough to rest for 10 minutes while preparing a lined baking sheet.

Drop rounded tablespoons of dough onto the baking sheet, leaving space in between. Bake for 11 minutes, then make shallow wells in the center and bake for 2 more minutes.

Cool on the baking sheet for 5 minutes before transferring to a wire rack.

In another bowl, whisk together heavy cream, powdered sugar, and cocoa powder until stiff peaks form. In another bowl, whisk pudding mix and milk until smooth. Fold together for mousse.

Fill each cooled cookie well with mousse and top with whipped cream and optional cocoa powder or chocolate curls.

Chill for at least 30 minutes before serving to allow mousse to set.