2/3 c. sugar
2 tbsp. cornstarch
2 beaten egg yolks or 1 beaten egg
1 tsp. vanilla
1/3 c. cocoa
2 c. milk or skim milk
2 tbsp. butter or margarine 

Combine sugar, cocoa, and cornstarch in 1 1/2 quart casserole. Blend together gradually stir milk into cornstarch mixture with wire whip. Cook on full power for 6 to 8 minutes, or until thickened and bubbling. Stir 2 to 3 times during cooking time. Beat half of hot mixture into egg yolks, return egg mixture to hot mixture. Cook on full power for 1 to 2 1/2 minutes, or until thickened and heated through. Stir twice during cooking time. Mix well with wire whip, stirring in butter and vanilla. Pour into 4 (6 oz.) custard cups or dessert dishes. TIP: To prevent boil overs, use large enough utensils. A general rule is: use a utensil twice as large as the amount of pudding to be cooked.
 

Source: http://www.nancys-kitchen.com