Preheat oven to 375 F. Combine rhubarb, 1/2 cup sugar, and flour in a non stick skillet. Cook over medium heat until sugar melts. Pour into bottom of prepared pie crust. Meanwhile, beat together cream cheese, 1/2 cup sour cream, and 1/2 cup sugar until fluffy. Add eggs one at a time, and 1 tablespoon vanilla until blended. Pour over rhubarb layer. Bake for 30 minutes or until puffed and golden. Combine remaining sour cream, sugar, and vanilla; spread over hot pie. Set on a wire rack to cool slightly; cover and refrigerate before serving.