01 -
In a small saucepan, combine brewed coffee, granulated sugar, and brown sugar over medium heat. Stir continuously until the sugars are fully dissolved.
02 -
Allow the mixture to reach a gentle simmer and cook for 5 to 7 minutes, reducing slightly while stirring occasionally.
03 -
In a separate bowl, whisk cornstarch with cold water until perfectly smooth.
04 -
Gradually whisk the cornstarch slurry into the simmering coffee mixture. Continue to cook, stirring constantly, until the sauce thickens, approximately 2 to 3 minutes.
05 -
Remove saucepan from the heat. Stir in unsalted butter, vanilla extract, and a pinch of salt until the sauce turns smooth and glossy.
06 -
Serve warm or allow the sauce to cool. Store any leftovers in an airtight container in the refrigerator for up to one week.