Using a vegetable peeler, carefully zest the orange in large strips, being careful to leave behind the white pith. Then juice the orange.
Combine zest, cranberries, sugar and orange juice in a saucepan.
Bring to a simmer, stirring to make sure sugar is dissolved. When mixture reaches a simmer, remove from heat.
Allow to sit for 20 minutes. Don't let it sit longer or it may become bitter. Strain to remove solids and store in a sealed container in the refrigerator .
Notes
If you want to make more syrup, double everything except for the orange zest, leave that the same.