Cajeta

Bring milk, sugar, vanilla, salt, and cinnamon stick, if using, to boil in Dutch oven over medium-high heat, stirring occasionally with rubber spatula.

Off heat, stir in baking soda mixture (milk will start to foam). When foaming subsides, return milk mixture to boil. Reduce heat to medium-low and simmer rapidly, adjusting heat as necessary to maintain rapid simmer and stirring occasionally to prevent scorching, until mixture is pale golden brown, 45 minutes to 1 hour.

Continue to cook, stirring frequently, until cajeta is caramel-colored and heavily coats back of spoon, about 30 minutes longer. Discard cinnamon stick, if using. If desired, strain cajeta through fine-mesh strainer. Cajeta can be refrigerated in airtight container for up to 2 months.