Bake cake in 13x9 pan according to package instructions. Allow to cool.
Using the end of a wooden spoon, poke holes in the top of the cake.
Pour chocolate pudding over the cake, making sure to pour over the holes. Alternatively, put the pudding mixture into a plastic candy decorating bottle or icing bag and squeeze directly into the holes in the cake for more even distribution.
Next, cream together cream cheese and powdered sugar. Mix in the unsweetened chocolate and 2 tablespoons of milk. Spread evenly over the cake.
Mix together whipped topping with 3 tablespoons chocolate syrup and ½ cup of chocolate chips. Spread this over the top of the cake and then top with additional chocolate chips, if desired, and drizzle with white chocolate sauce.