Combine the cocoa, sugar, salt and cornstarch in a saucepan and mix well.
Slowly add the Silk, whisking constantly to prevent lumps. Bring this mixture to a boil over medium heat while whisking constantly.
Lower the heat to a simmer, cover and simmer gently for 8-10 minutes, until pudding begins to thicken.
Remove from the heat and whisk in the margarine (or butter) and vanilla.
Pour into 1 large bowl or 8 small serving bowls and refrigerate for at least an hour until thoroughly chilled.