Start by infusing the milk. In a medium-sized saucepan over low heat, mix together the milk, cinnamon sticks and nutmeg. Let this mixture cook for 25 minutes. (Make sure the heat is at the absolute lowest setting or the milk will burn)
While the milk is being infused, add the egg yolks to a large bowl and give them a whisk for a few seconds to break the yolks. After the milk has infused for 25 minutes, use a slotted spoon to remove the cinnamon sticks from the saucepan.
Temper the egg yolks. While simultaneously whisking the egg yolks, pour a little bit of the hot milk mixture into the bowl. After you've incorporated about ½ cup of the hot milk, keep whisking the yolks and pour in the rest of the hot milk mixture into the bowl in a slow and steady stream. **When you're tempering yolks, it's best to introduce a little bit of the hot liquid at a time while you're whisking the yolks to keep them from turning into scrambled eggs.** Once all of the hot milk mixture and the yolks have been whisked together, whisk in the condensed milk, vanilla extract, a pinch of kosher salt, the brandy (or silver rum) and the hazelnut liqueur.
Let your rompope cool completely before funneling it into a bottle, then let it chill in the fridge. Serve over ice with a pinch of ground cinnamon and enjoy!
Note: The flavors in rompope will intensify as it sits. I like to serve mine over ice after it's chilled in the fridge for at least 3 days. (If anything settles in the bottom, just give it a quick shake before serving)