In small saucepan over high heat, bring 1 cup blackberries, sugar, cornstarch, sea salt and water to boil, crushing berries with back of wooden spoon to release juices. Continue to boil, stirring constantly, 2 to 3 minutes until mixture is thickened. Transfer to large bowl; cool 5 minutes. Stir in remaining blackberries. Cool 15 minutes, then spoon evenly over pie. Refrigerate 30 minutes to set slightly before serving.