Preheat oven to 350° F. Steam the potatoes in a steamer basket in a large saucepan until tender, 15 to 20 minutes.
In a food processor, puree sweet potatoes with heavy cream, sugar, butter, eggs, cinnamon, and salt until smooth.
Pour the mixture into the piecrust and bake until the center is set but still slightly wobbly, 40 to 50 minutes. Let cool.
Dust with confectioners’ sugar before serving.