GREASE 8-inch-square baking pan.
COMBINE cookies, candy, morsels and butter in small bowl. Spread onto bottom of prepared baking pan. Refrigerate for about 10 minutes.
PREPARE mousse mix according to steps 1 and 2 of package directions; spread over cookie crust. Freeze for about 30 minutes or until set. Let stand at room temperature for about 5 minutes before cutting into 4 X 1-inch rectangles.