In a small bowl, sprinkle 1 1/2 teaspoons gelatin onto 2 1/2 tablespoons cold water. In another bowl, toss together 2 cups sliced strawberries, 3 tablespoons sugar and 2 teaspoons balsamic vinegar; let sit. Meanwhile, in a small saucepan, heat 1 cup half-and-half with 6 tablespoons sugar over medium heat, stirring, until the sugar has melted. Whisk in 1 1/2 teaspoons vanilla extract and the softened gelatin, then whisk in 1 cup sour cream. Transfer to a bowl and refrigerate until set, about 2 hours. Top with the strawberries in balsamic syrup and a few fresh basil leaves.