1. Bake pie crust in a 4- x 14-inch tart pan according to package directions until golden; cool completely on wire rack.
2. Beat sour cream and next 5 ingredients in a large bowl. Spread mixture evenly into cooled pastry shell. Arrange berries on top. Garnish, if desired. Chill 2 hours for easiest slicing.
To fit the round refrigerated pastry into a rectangular tart pan, place pastry into pan, and trim off edges. Piece together trimmings with pastry in pan to complete rectangle, and brush edges with beaten egg to seal.