In the large heavy-bottomed pan, stir in all the ingredients except the baking soda. Bring this mixture to a simmer, constantly and vigorously stirring to dissolve the sugar fully and prevent burning.
Once the mixture is simmering, quickly remove the pot from the heat then add the baking soda. You’ll immediately see the mixture rise and froth up. Continue stirring.
When the mixture stops bubbling, place the pot back on the stove over medium heat and keep stirring every five minutes. Ensure that the milk mixture doesn’t scorch at the bottom and stays at a simmer.
After about 1 hour to 1 hour and 30 minutes, the milk mixture will slowly turn a golden brown. Remove the vanilla bean pod and the cinnamon stick. Increase your stirring frequency. Frequent continuous stirring will prevent the mixture from burning
Your Cajeta is done when the mixture has turned a rich brown and coats the back of the ladle, a thickness resembling that of honey. Let cool then pour into airtight containers.
Like the goat milk cheese, your Cajetas will keep for a week in the fridge.