Place the pastry in a 10" deep dish and trim off edges. Arrange rhubarb into shell and scatter strawberries around. Mix the sugar and 1/3 cup of flour together. Stir in the sour cream and pour evenly over the rhubarb strawberry mixture.
Combine the butter, 1/2 cup flour and brown sugar until crumbly. Sprinkle on top.
Bake for 15 min. at 450F, then an additional 30 min. at 350F or until fruit is tender and crumbs are golden brown. Cool completely before serving.