In a large bowl, combine the hot sweet potatoes; mash with butter. Stir in sugar and allow to cool slightly.
Beat in the egg yolks one at a time, mixing thoroughly after each addition. Blend in cream and vanilla. Pour into pie shell and dust top with grated nutmeg.
Bake 10 minutes at 400 degrees F (200 degrees C). Reduce oven temperature to 375 degrees F (190 degrees C), and bake until center is set, about 35 minutes more.