In mixing bowl, beat together cake mix, oil and egg. Stir in chocolate chips, white chocolate chips and toffee bits. Press half of batter into baking pan. Bake 10 minutes. Remove from oven.
While crust is baking, melt butter, caramels and condensed milk over med-low heat until caramels have melted and mixture is smooth. Pour slowly and spread evenly over crust. Drop remaining batter in spoonfuls over the top.
Return to oven. Bake 25-30 minutes or until top is set and edges are golden brown. Cool 20 minutes. Loosen edges from pan and continue to let cool for 40 minutes. Refrigerate 1 hour. Cut into small squares to serve.