on a cold countertop, make a mound of the flour with a dip in the middle. Put the butter, salt and 1 tsp of the sugar into the dip and use a fork to blend. Gradually add in the ice water as needed (different kinds of flour absorb water differently).
Ball the pie crust dough and put it in the fridge wrapped in cling wrap.
Boil the yams until soft and strain the water.
Put all the pie filling ingredients together in a blender and blend until consistent.
Roll out the pie crust and lay into a pie pan. Pour the filling into it.