Preheat the oven to 350°F Spray a 9-inch square baking pan with vegetable spray.
Make cake: in small microwavable bowl, combine the chocolate chips and water. Cook on high for 30 seconds or just until the chips beging to melt. Stir the mixture until it is smooth.
In a large bowl and using a whisk or electrical mixer, beat sugar, cocoa, egg, egg whites, sour cream, corn syrup, oil, vanilla and melted cholate.
In another bowl, stir together the flour and baking powder. With a wooden spoon, stir the dry ingredients into the sour cream mixture just until everything is combined. Pour the mixture into a prepared pan.
Place the pan in the centre of the oven and bake for 30 to 35 minutes or until a tester comes out dry.
Let the pan cool on a wire rack.
Make icing: in a bowl and using a whisk or electric mixer, beat icing sugar, cocoa and water until the mixture is smooth. Spread it over the cake.