In a mixing bowl, combine flour and butter for the crust. Add ice water and mix until dough forms. Divide dough in half, roll out one half and fit into a pie dish.
In another bowl, mix rhubarb, sugar, and flour for the filling. Pour into the pie crust and dot with butter.
Roll out the second half of the dough and place over the filling. Seal and flute the edges. Cut small slits in the top crust.
Bake for 50 minutes or until crust is golden and filling is bubbly.