Zest oranges, then cut them in half and squeeze to juice them.
Combine orange zest and juice (about 1/2 c.) in a medium saucepan.
Add remaining ingredients and heat over medium heat, stirring constantly.
After about 5 minutes the mixture should start to boil gently.
Continue boiling, stirring constantly 3-4 minutes more.
Remove from heat and cool to room temperature before using.
Store in an airtight container in the refrigerator.