Preheat oven to 350 degrees F. Line a 13x9" baking pan with foil, extending the sides of the foil over the edges of the pan. Mist the foil liberally with cooking spray and set aside.

In a large bowl, combine the cake mix, egg, melted butter and vanilla until a soft dough has formed. Spread the dough into the prepared pan in an even layer and bake for 12 minutes.

Remove the pan from the oven but keep the oven on. Gently lay the Pop Tarts across the surface of the dough in an even layer, breaking Pop Tarts to fit if needed. Top the Pop Tarts layer with pieces of sugar cookie dough, the chopped sugar cookies, the chopped Peeps candies, and the white chocolate chips as evenly as possible. Drizzle evenly with the sweetened condensed milk.

Return to the oven and bake for an additional 18-20 minutes or until the top is lightly golden and the center appears just about set. Sprinkle with additional sugar if desired. Cool in the pan completely, then gently lift the bars out of the pan using the foil sides and cut into squares. I like letting my bars sit overnight for an easier cut.