Preheat oven to 180 C / Gas 4. Grease a 20x30cm baking tin.
In a large bowl, mix together the cake mix, melted butter and 1 egg until smooth. Batter will be thick. Spread evenly into the bottom of the prepared tin. Next, sprinkle the chocolate chips over the layer of batter. Finally, beat the cream cheese, 2 eggs and icing sugar together in a medium bowl until smooth. Pour as evenly as you can over the chocolate chips.
Bake for 35 to 40 minutes in the preheated oven, until the top is set. Let cool for at least 30 minutes before cutting into bars.