Preheat oven to temperature indicated on box. Line a baking pan with parchment paper or aluminum foil and spray it well with cooking spray.
Prepare mix according to package directions, stirring half of the candy into the batter. Transfer to a baking dish and sprinkle the remaining candy and crushed cookies over the top.
Bake according to package directions, until a toothpick inserted in the center comes out clean. Cool completely before cutting.
Heads up: Cutting these guys gets a lot easier if you refrigerate them once they’re cool – they’re also deliciously fudgy when served cold!