Mix all the ingredients for the pie crust to a smooth dough and let it rest in the fridge for 1 hour.
Cover the bottom and the edges of a pie form with the pie crust. Let it lest in the fridge until it is time to put it in the oven.
Preheat the oven at 200 degrees Celsius
Peel and cut the rhubarb in small pieces.
Crumble the graham biscuits on the bottom of the pie crust.
Place the rhubarb on top of the biscuit crumbles.
Place the pie crust in the middle of the oven for 20 minutes.
Take out the pie crust from the oven and place it on the side for the moment.
Beat the egg together with the sugar, add the cème fraiche and pour it over the rhubarb. Place the pie in the oven for another 15 minutes.