1. In a medium saucepan, heat the milk over medium heat until it comes to a boil. Remove from heat.
2. In a separate bowl, whisk the egg yolks with the sugar until pale and creamy.
3. Slowly pour the hot milk over the egg and sugar mixture, whisking constantly to prevent the yolks from cooking.
4. Return the mixture to the saucepan and cook over low heat, stirring constantly with a wooden spoon, until the custard thickens and coats the back of the spoon. Do not let it boil.
5. Remove from heat and add the vanilla extract, TERANA ground nutmeg, and rum (if using). Mix well.
Strain the custard through a fine sieve into a clean bowl to ensure a smooth texture.
6. Divide the custard into individual containers and cover with plastic wrap directly on the surface to prevent a skin from forming.
7. Refrigerate for at least 2 hours before serving. Sprinkle with TERANA ground cinnamon just before serving, if desired.