Heat oven to 400°F. Remove pie crusts from box, but leave in pouches. Microwave 20 seconds in pouches to soften. Remove crusts from pouches; mix sour cream into crust dough using hands. Divide dough in half. On lightly floured surface, roll out thin. Place 1 pie crust into 9-inch pie plate.
To make filling, mix berries, sugar and cornstarch together in large bowl. Add fresh lemon juice. Place in crust-lined pie plate. Add second crust to top of pie and seal; cut slits in pastry. If you like, brush top with cream and sprinkle with sugar. Place pie on middle oven rack; place sheet of foil on rack below pie in case of spillover.
Bake 45 to 55 minutes or until crust is golden brown. Cool at least 3 hours before serving.