In a medium saucepan over medium heat, combine raspberries, sugar and 1 tbsp. water.  Bring mixture to a boil.  Combine cornstarch and 2 tbsp. cold water in a small bowl to create a slurry.  Add cornstarch slurry to raspberries.  Stir to combine.  Continue to stir until raspberry mixture is thick.   Remove from heat and allow to cool completely before using.