In a large pot, mix the milk with the sugar. Bring to a simmer over medium heat stirring occasionally until the sugar dissolves.

Add the vanilla extract and the baking soda. Lower heat to low and simmer uncovered for about 1½-2 hours or until you reach a rich brown, caramel color and it has reduced to about one cup (236 ml). Stir occasionally and remove the extra foam that forms on top.

Strain any clumps with the help of a strainer. You can store it in the refrigerator in an airtight container for up to one month.