Gently mix together the ground cherries, sugar, tapioca, flour and lemon juice.
Let stand for 15 minutes.
Preheat the oven to 450 degrees F (230 degrees C). Line a 9 inch pie pan with half of the pastry.
Pour the fruit mixture into the pastry-lined pan, and dot the top with the butter. Cover with top crust or lattice.
Bake at 450 degrees F (230 degrees C) for 10 minutes, then reduce the heat to 350 degrees F (175 degrees C) and bake for another 40 minutes, or until golden brown.