Combine puree and sugar in a heavy-bottomed pot and bring to a boil over medium-high heat. Reduce to a low simmer and cook, stirring frequently until thickened, about 4-5 minutes. (Syrup should heavily coat the back of a spoon, and leave clean streaks in the pan when a spatula runs through it).

Allow to cool, then transfer to a jar or squeeze bottle and refrigerate until ready to use.