to add a little of the latter to prevent the sauce from becoming too bitter. Although it's thin when taken off the stove, the sauce thickens as it chills. Store it in an airtight container in the refrigerator for up to 2 weeks.
Combine first 6 ingredients in a small saucepan, stirring with a whisk until blended. Bring to a simmer over medium heat. Reduce heat; simmer 6 minutes, stirring occasionally. Remove from heat; stir in vanilla. Cover and chill.