In a small bowl, lightly beat the egg whites. Set aside.
In a large bowl, add the unsweetened cocoa and the cornstarch.
Add half of the skim milk to the cocoa mixture. Save the remaining half of the skim milk for later.
Whisk the skim milk and the cocoa mixture until smooth. Set aside.
In a large heavy pot, add the remaining half of the skim milk, sugar, and salt. Mix well.
Set the pot on the stove, turn the heat on high, and bring the skim milk mixture to a boil. Whisk constantly, then remove from the burner.
Immediately dump the cocoa mixture into the pot with the hot skim milk mixture, whisking constantly.
Put the pot back on the burner on medium-high heat. Bring the mixture to a boil whisking constantly. Boil for 2 minutes, then remove the pot from the burner.
Gradually whisk the egg whites into the cocoa mixture.
Put the pot back on the burner on medium-low heat. Cook for 2 minutes, whisking constantly, but do not boil. Then, remove the pot from the burner.
Add the vanilla extract to the chocolate pudding mixture. Blend well.
Pour the chocolate pudding into serving bowls.
Cool to room temperature or chill in the refrigerator for about 1 hour.
Notes
When making pudding, stir constantly so the mixture doesn't burn on the bottom of the pan.
Top the chocolate pudding with strawberries, cocoa, whip cream, coconut flakes, crushed Oreo cookies, coconuts flakes, slivered almonds, or chocolate flakes.
You can cover each bowl of pudding with plastic wrap or waxed paper to prevent the pudding from forming a film on top.