Toss the 1 pound strawberries, ½ cup granulated white sugar, 1 tablespoon balsamic vinegar, 1 teaspoons vanilla extract, and ⅛ teaspoon kosher salt together in a glass baking dish. Spread the mixture out so the strawberries are in a single layer.
Roast in the oven stirring every 30 minutes until the jam reduces and the juice almost completely evaporates. Approximately 1 ½ 2 hours depending upon the water content of the strawberries. Watch closely toward the end of the cooking time. As the sugar concentrates the jam will burn more easily.
Remove from oven and let cool to room temperature. Once completely cool, mash to break up larger chunks of strawberry and store in an airtight container in the refrigerator.
Notes
The jam will thicken as it cools and the natural pectin present in strawberries sets.If you are planning to freeze the jam, make sure you leave space at the top of the jar for expansion during freezing. Storage: Roasted strawberry jam can be stored in an airtight container in the refrigerator for up to 2 weeks or for up to 6 months in the freezer.Thaw frozen jam overnight in the refrigerator.