I've eaten pumpkin pie all my life, but never encountered its close cousin the Sweet Potato Pie until I moved south as a young adult. They're very similar, but I've developed a *slight* preference for the sweet potato (which is available year-round, unlike fresh pumpkin).

The recipes are probably similar if not identical, substituting mashed yams for canned or fresh-mashed pumpkin.

A few years ago, at Thanksgiving or Christmas, my wife Peggy discovered a recipe for Double Pumpkin Pie, with a layer of the regular pumpkin-custard filling topped with a second layer of pumpkin mousse, the same stuff mixed with beaten egg white and maybe some other stuff, creating a layer of filling lighter in color and in texture from the bottom layer -- kinda like the meringue topping on a lemon-custard pie. She usually puts these fillings into a cracker-crumb crust -- either graham crackers or vanilla wafers. Needless to say, this delicacy has become a feature of *every* holiday dinner since.

FYI: Here in the US, a mixture of cinnamon, ginger, nutmeg, and probably ground cloves is commonly labeled and marketed as "Pumpkin Pie Spice."