Preheat oven to 350°.
Combine skim milk and candies in a bowl. Microwave at HIGH 1 1/2 to 2 minutes or until caramels melt and mixture is smooth, stirring with a whisk after every minute. Set aside.
Combine sweetened condensed milk, cake mix, margarine, and egg white in a bowl; stir well (batter will be very stiff). Coat bottom only of a 13 x 9-inch baking pan with cooking spray; dust lightly with flour. Press two-thirds of batter into prepared pan using floured hands; pat evenly (layer will be thin).
Bake at 350° for 10 minutes. Remove from oven; sprinkle with chocolate chips. Drizzle caramel mixture over chips; carefully drop remaining batter by spoonfuls over caramel mixture. Bake at 350° for 25 minutes or until done. Let cool completely in pan on a wire rack.