Preheat oven at 350°F, then in large bowl, combine cake mix, pudding mix, chocolate chips. In a separate bowl combine milk, eggs and vanilla extract. Add egg mixture to dry mixture and mix by hand until blended. Pour into a greased 10 inch (3 quart) bundt pan. Bake for 50-55 minutes, cool for 15 minutes, remove from pan.
Combine cocoa, water, oil and cornstarch in a saucepan; cook over low heat until smooth. Add sugar; mix well. Drizzle warm glaze over cooled cake.