* Heat oven to 450F.
* Press pie crust into a 9" pie pan.
* Spread rhubarb in an even manner over the bottom of the crust.
* In a medium sized bowl, whisk egg, white sugar, sour cream and 1/3 cup flour until smooth. Pour over rhubarb.
* In a small bowl, mix 1/2 cup flour and brown sugar. Stir in melted butter until mixture is crumbly. Sprinkle over the top of the pie.
* Bake for 15 minutes, then reduce the heat to 350F.
* Continue to bake for 40 minutes, or until edges have puffed, and topping is golden.
* The centre might be still somewhat jiggly, but once it is cooled completely it is perfect to slice and serve!