Add a thickener made of cornstarch, tapioca starch or flour and water:
Mix 2 tsp. starch/flour with 2 Tbsp. cold water in a small bowl. Add to hot mixture and bring to a boil for 1 minute.
Add larger amounts of this mixture in similar proportions for larger amounts of sauce. Adjust seasoning after thickening.
Cornstarch and tapioca starch give a clear finish to a sauce, whereas flour gives an opaque finish.