Heat the oven to 425 degrees.
Place the cream cheese in a large bowl and mix on high speed with electric mixer until soft and fluffy.
Add the sugar and continue to mix on high speed until completely absorbed.
Reduce the mixer speed and add the eggs, one at a time, until evenly blended.
Add the yams, evaporated milk and pumpkin pie spice, and mix until creamy.
Pour the filling into the pie shells.
Bake pies for 30 to 35 minutes until the edges puff, the crust browns and the custard is set.
Meanwhile, mix the pecans, brown sugar and butter; set aside.
Remove the pies from the oven and sprinkle with the pecan mixture.
Return the pies to the oven for 7 to 10 minutes or until the topping is golden brown and crisp.
Cool the pies completely on a wire rack. Serve garnished with whipped cream.