Process berries in a blender or food processor 30 seconds or until smooth. Press through a fine wire-mesh strainer into a saucepan; discard pulp and seeds.
Stir together sugar and cornstarch in a small bowl, and add to pureed raspberries; stir in vanilla. Bring raspberry mixture to a boil over medium heat, stirring occasionally. Cook, stirring often, 2 minutes; remove from heat. Pour into a small bowl or cruet; cover and chill 1 hour.