Warning: this pie has a tart and tangy filling that might not be sweet enough for some people. That said, I love the tangy quality of this filling and wouldn’t want it to be any other way. By the way, since the filling is cooked before the pie is baked, you can taste it and add a little more sugar if you want. My late friend Joseph Viggiani shared this recipe years ago; I have no idea where he might have found it.