Cook the prunes slowly in water to cover until they are tender, about 30 minutes. Drain them, reserving 1/2 cup of the juice.
Preheat the oven to 425°F.
Line a pie pan with half the pastry dough. Pit the prunes and cut them in quarters. Mix the reserved prune juice, sugar, flour, lemon rind, and lemon juice in a small bowl.
Spoon the prunes into the lined pie pan and pour the juice evenly on top. Dot with the butter. Roll out the remaining dough and make a lattice top. Crimp or flute the edges.
Bake for 10 minutes, then lower the heat to 350°F and continue baking for about 35 minutes or until the crust is browned.