In a blender, combine 1 cup blueberries and corn syrup; cover and process for 30 seconds or until blueberries are almost smooth.
Place cornstarch in a small saucepan; gradually whisk in the blueberry mixture. Bring to a boil over medium heat; cook and stir for 1 minute or until thickened. Remove from the heat; stir in the remaining blueberries and cool. Store in the refrigerator.