Mash 1 cup raspberries and press through a strainer. Reserve enough juice to measure 1/4 cup. Discard seeds and pulp. In a small saucepan, combine sugar and cornstarch; stir in reserved juice until smooth. Add strawberries and cook over low heat until mixture comes to a boil; cook and stir for 1 minute or until thickened. Remove from the heat; stir in lemon juice and remaining raspberries; cool.
In two parfait glasses, layer half the ice cream, a fourth of the berry sauce, half the sour cream and a fourth of the berry sauce. Repeat layers.