From Elizabeth Jacob's cookbook, written in 1654 (or possibly later)
A Potatoe Pye
Boyle them and peel them lay them in your pye, take marrow dipt in the yolks of eggs, then bake the rowles of marrow with some cinamon and lay them in slices in the pye with some lemon and orange peel candied and Apricocks and barberries on the tope of the pye before it be lided lay on sugar and buttor, one how or bakes it.
The English manuscript itself is dated to 1654, but this may be simply a starting date for the book. Regardless, I do enjoy finding a good early recipe for things like potatoes... especially as the subject of potatoes continues to come up in various conversations about earlier cookery.
I could see such a recipe being quite a hit if made with sweet potatoes though I am distantly reminded of layered pies of sweet spices and cheese with either turnips or apples from the 15-16th centuries. One obviously being a sweet fruit while the other is an almost bitter root, yet both work quite well... I actually prefer the turnip variation.
(note: turnip, not rutabaga and sweet potato, not yam)
This recipe does, however, simply states "potatoe" so draw your own conclusion... it is certainly late enough to be a perfectly plausible potato pie. Though quite possibly a sweet potato pie, num!