In a medium sauce pot whisk together the sugar, cocoa powder, cornstarch, salt and cinnamon.
Whisk in beaten eggs followed by milk. Cook over medium heat, whisking constantly, until bubbly and thickened.
Remove from heat, whisk in chocolate, butter and vanilla.
Strain into a bowl or a plastic lined baking sheet. Cover the surface with plastic wrap and poke a few holes to allow steam to escape. Cool to room temperature and then refrigerate at least 2 hours.
Pipe into desired molds or bowls.
Alternatively you could put the hot pudding directly into the final container (cups or decorative bowl), but cover the surface with plastic wrap and then refrigerate. It will take longer to cool.
Optional Topping: whipped heavy cream and crushed Oreo crumbs!