Preheat the oven to 175°C (350°F) and line a baking sheet with parchment paper.
In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth.
Add the vanilla and egg, mixing until just combined.
In a separate bowl, whisk together the flour, baking soda, and salt. Add to the wet ingredients and mix until just combined.
Fold in the chopped chocolate and ¾ of the crushed Oreos.
Scoop about 1 tablespoon of dough and flatten it slightly. Place a whole Oreo in the centre, then top with another 1-2 tablespoons of dough, sealing the edges.
Roll each stuffed cookie in the remaining Oreo crumbs for extra crunch.
Place on the baking sheet about 7cm (3 inches) apart. Bake for 8-10 minutes, until the edges are golden and the centres are just set.
Cool on the tray for 5 minutes before transferring to a wire rack to cool completely.