Bring all ingredients except vanilla to boil in 5- to 6-quart Dutch oven on medium-high heat, stirring frequently. (It is important to keep stirring to prevent mixture from boiling over.) Reduce heat to medium-low; simmer, stirring occasionally, 30 minutes or until sauce is reduced by half, coats the back of a spoon and is a deep brown caramel color.
Carefully strain cajeta into medium heatproof bowl. Stir in vanilla. Cool to room temperature. Cover. Store in refrigerator up to 2 weeks. If desired, warm cajeta in microwave oven before serving.