Prepare masa (see recipe link above). You can also use Masa Instantanza if you wish. Prepare according to the package directions.

In a large bowl, combine the masa, brown sugar, and vanilla until well blended.

To assemble the tamales, place 1/2 cup of the masa in the center of the smooth side of a corn husk. Using the back of a wet tablespoon, make an indentation in the center of the masa and fill with 1 1/2 tablespoons or more of the chocolate chips.  Fold both sides of the husk tightly in over the masa mixture and tie a t both ends.  Repeat for the reaming tamales.  Steam the tamales for 55 minutes.  Serve plain or with whipping cream.

The Book
Tamales 101 by Alice Guadalupe Tapp. This is a great book for the beginner or seasoned tamale maker. 

Recipes include Chicken Tomatillo, Chorizo Potato, Vegetable Curry, and Greek tamales. Nearly 100 traditional, vegetarian, vegan, and specialty tamales and sauces. Available in our Gourmetsleuth.com catalog.