Preheat oven to 350 degrees F. Line a 13×9 inch pan with foil, extending the sides over the edge of the pan. Mist lightly with cooking spray and set aside.

In a large bowl, combine the cake mix, melted butter, and egg until blended. Stir in the chopped pretzels. Press the mixture evenly into the prepared pan and bake for about 12 minutes.

Remove the pan from the oven and sprinkle on the crushed Oreos, chopped Kisses, chopped candy bars and squares, and the baking chips in an even layer. Drizzle evenly with the sweetened condensed milk.

Return to the oven and bake for an additional 15 minutes or until the center is set and slightly bubbly.

Cool the bars completely in the pan before cutting into squares. Store at room temperature, airtight, up to 3 days.