Preheat oven to 325°. Coat a 9″x 13″ baking pan with cooking spray. Line pan with foil, letting ends hang over the short sides of the pan. Coat foil with cooking spray.
Whisk together flour, cocoa, baking powder, baking soda, and salt. Set aside.
Using an electric mixer, beat butter, sugar, and brown sugar until smooth. Add eggs, Kahlua, and vanilla. Beat just until blended. Gradually add flour mixture, beating until blended. Stir in Oreos, chopped candy bar, chocolate chips, white chocolate chips, and pecans.
Spread batter evenly in prepared pan. Bake 55-58 minutes.
Cool in pan on wire rack. Cover and chill for at least 2 hours before removing from pan and cutting into bars.