In a heavy saucepan over medium heat add milk, sugar, dark corn syrup, and cinnamon stick and stir.
Bring to a simmer, stirring occasionally, until the sugar has dissolved. Once the sugar has dissolved, add the baking soda and stir to combine.
Reduce the heat to low and cook uncovered at a low simmer. Stir occasionally, but do not re-incorporate the foam that appears on the top of the mixture.
Continue to cook until the mixture is a dark caramel color and has reduced to about 1 cup, approximately 1 ½ to 2 hours.**About an hour into the process, stir more often to prevent the milk from burning.
Remove from heat and transfer to a bowl to cool.
Store in the refrigerator in a sealed container for up to a month.
Dulce de Leche by lifeonwesterlycreek on Jumprope.