Step 1In a heavy saucepan, combine the sugar and leaves, rubbing the leaves with the sugar until the leaves are softened and have released their oils. Add the berries, and any berry juice, to the saucepan. Simmer the mixture over medium-low heat, stirring frequently, until the berries are thickened to jam and reduced to 3 generous cups, about 25 minutes. Stir in the lemon juice. Transfer to jars and cool completely. Seal and refrigerate. The jam will keep, covered and refrigerated, up to 1 month.