How to Make It
In a small saucepan, combine the milk and 2 tablespoons of the sugar and heat until steaming and the sugar is dissolved. Put the egg yolk in a small bowl and gradually whisk in the hot milk. Return the mixture to the saucepan and cook over moderate heat, whisking constantly, until slightly thickened, about 2 minutes.
Off the heat, add the chopped chocolate and salt and whisk until smooth. Whisk in the butter. Pour the custard into 2 shallow bowls and refrigerate briefly, about 5 minutes.
Meanwhile, in a medium bowl, beat the heavy cream with the cinnamon and the remaining 1 tablespoon of sugar until softly whipped. Dollop the cream on the custards, sprinkle the chocolate shavings on the cream and serve.