Preheat oven to 350 degrees.
In a large pot, cut sweet potatoes crosswise into 1-inch thick chunk and steam until tender -- about twenty to twenty-five minutes. (If using yams from can simply pour into a large bowl and continue.) Using an egg beater, beat the sweet potatoes until they are smooth or puree them in a food processor.
In a large bowl, mix together eggs, sugar, butter, spices, vanilla, and liqueur.
Pour batter into pie crust.
Bake for thirty minutes.
Accompany with whipped cream or French vanilla ice-cream.