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, oil and strawberry extract, if using, until a soft dough forms. Press the dough evenly into the prepared pan and bake for approx. 12 minutes.

Remove the pan from the oven but keep the oven on. Evenly distribute the chocolate chips, white chocolate chips, chopped chocolate squares, marshmallows and Oreos onto the dough. I like putting the marshmallows on first so they're covered - it prevents them from burning and expanding as much. Drizzle evenly with the condensed milk.

Bake for approximately 20-22 minutes or until center appears set and the top is golden brown and bubbly. Cool completely (I recommend overnight) before lifting out of the pan and cutting into squares. Garnish with sprinkles, if you'd like!