Preheat oven to 350 degrees. Spray a 9 x 13 inch pan with PAM. In large bowl, stir together melted butter and brown sugar until smooth. Beat in eggs and vanilla until evenly combined. Add flour until combined. Spread in prepared pan. Sprinkle coconut over blondie base then drizzle condensed milk on top of coconut. Sprinkle the top with rainbow sprinkles.
Bake for 25-30 minutes or until set. Let cool before cutting.