1 quart whole milk
12 ounces sugar, approximately 1½ cups
1 vanilla bean, split and seeds scraped
½ teaspoon baking soda
1. Combine the milk, sugar, vanilla bean and seeds in a large, 4-quart saucepan and place over medium heat. Bring to a simmer, stirring occasionally, until the sugar has dissolved.
2. Once the sugar has dissolved, add the baking soda and stir to combine. Reduce the heat to low and cook uncovered at a bare simmer. Stir occasionally, but do not re-incorporate the foam that appears on the top of the mixture. Continue to cook for 1 hour.
3. Remove the vanilla bean after 1 hour and continue to cook until the mixture is a dark caramel color and has reduced to about 1 cup, approximately 1½ to 2 hours.
4. Strain the mixture through a fine mesh strainer, and store in the refrigerator in a sealed container for up to a month.