In a small bowl, lightly beat egg whites and set aside. In a large bowl, combine 2/3 cup of cocoa and cornstarch. Whisk 3/4 cup of milk into cocoa mixture until completely smooth.

In a large heavy suacepan, combine remaining milk, sugar and salt. Mix well. Bring to a boil over high heat, whisking constantly. Remove pan from heat.

Whisk cocoa mixture into hot milk mixture. Bring to a boil over medium-high heat, whisking constantly. Remove pan from heat.

Gradually whisk 1 cup of hot cocoa mixture into the egg whites. Pour mixture back into the pan. Cook over medium-low heat for 2 minutes, whisking constantly. Do not boil. Remove pan from heat.

Add vanilla; blend well. Pour pudding into serving dishes. Cool to room temperature. Cover and chill for 1 hour. Garnish with berries, mint leaves and cocoa.