There is a wonderful chain of shops in France, La Chambre Aux Confitures, that is well known for their unique flavor combinations, like peach-lemongrass, strawberry-verbena, and raspberry-geranium, just to name a few. I was inspired by this shop to blend sweet blueberries and tart lime for a new twist on classic blueberry jam.
Combine the blueberries, sugar, lime zest, 3 tablespoons lime juice and the salt in a medium saucepan or Dutch oven. Toss well and let stand until the sugar dissolves and the blueberries begin to release their juices, about 15 minutes.
Bring the mixture to a rapid simmer over medium-high heat. Reduce the heat to maintain a low simmer; cook, stirring often and skimming off any foam, until the blueberries are tender and the juices thicken, about 35 minutes. Add the remaining 1 tablespoon lime juice. Remove from the heat and let the jam cool to room temperature, stirring occasionally, about 1 hour.
Transfer the jam to a jar or other airtight container. Refrigerate until cold and fully jelled, 3 to 4 hours. Store in the refrigerator for up to 2 weeks.