21 fl. oz. Condensed Milk
18 oz. Sweetened Condensed Milk
3/4 tsp. Baking Soda
3/4 tsp. Vanilla Extract
1 oz. Light Corn Syrup
1.) In a large sauce pot (copper bottomed suggested) over medium heat, combine milks and soda. Bring to a low boil, whisking constantly (will foam over if not careful). Reduce to a low heat, whisking until foaming stops and volume decreases.
2.) Continue cooking on low heat, and reduce by 1/3 (about 45 minutes), stirring occasionally to prevent scorching. The sauce should be a medium caramel color. To check for readiness, place a small amount on a spoon and allow to cool; ready when sauce becomes thick.
3.) Remove from heat, stir in vanilla. Cool completely, stirring occasionally. Store in an airtight container at room temperature.