Roll out pastry and set aside. Bring water to a boil in a large saucepan.
In a small bowl mix together sugar and cream of tartar. Add mixture to boiling water. Stir, then add crackers, one at a time. Boil for 3 minutes, but do not stir.
Pour cracker mixture into pastry-lined pie pan. Sprinkle crackers with cinnamon and dot with butter or margarine. Cover with top pastry. Seal edges and cut steam vents in top.
Bake in preheated oven for 30 minutes, until crust is golden brown. May need to cover top pastry partway through baking to prevent overbrowning.
