Heat the milk with the cinnamon over medium heat. Keep your eye on it, because it heats up fast.
While the milk is warming up, dissolve the gelatin in a cup of cold water. You’ll see how the liquid turns into a gel.
When the milk just starts to boil, lower the temperature, add the gelatin and let it dissolve well. Turn off the heat, add the condensed milk and stir until it’s completely mixed together. Let it cool off for 10 minutes or until it’s lukewarm.
Strain the milk into a pitcher in order to remove the cinnamon stick then pour it into a gelatin mold or into individual glasses.
Put it in the refrigerator until it’s firm. This will take several hours. I recommend preparing it the night before so that it can cool all night or preparing it early in the morning the day you plan to serve it.
To remove it from the mold, with a knife or ice pick, carefully separate the gelatin from the mold’s wall. Heat water and pour it into a deep bowl. Submerge the mold with the gelatin for a few seconds. Put a plate on top and with a quick and precise movement, flip it over.
Carefully remove the mold.