Preheat oven to 300°F (150°C).

In a mixer bowl, cream together the softened butter and sugar until light and fluffy.

Add the milk and mashed sweet potatoes alternately, beating well after each addition to ensure a smooth consistency.

Beat in the grated orange rind and ginger until evenly distributed.

Pour the sweet potato mixture into the unbaked 9-inch pie shell.

Bake in the preheated oven for 45 minutes, or until the filling is set and the pie crust is golden brown.

Remove from oven and let cool slightly.

Serve warm with a dollop of whipped cream.