Grease and flour a 9 x 13-inch pan. Heat oven to 350 degrees F.
Cake: Combine cake mix, water, sour cream, oil and eggs and beat at low speed
until moistened. Beat for 2 minutes at high speed.
Stir in chocolate chips. Pour batter into pan.
Bake for 45 to 55 minutes or until cake springs back when touched lightly
Serve cake slightly warm or cool with Custard Sauce.
Custard Sauce: Combine milk, eggs, sugar and salt. Blend well. Cook over
medium-low heat until mixture coats the back of a spoon; stir constantly. Do not boil. Custard sauce needs slow cooking.
It will curdle if boiled. Remove from heat; stir in vanilla extract.