1 1/2 pounds sweet potatoes, cleaned and left a bit damp
1/2 cup plus 3 tablespoons heavy cream
1/3 vanilla bean, split lengthwise and seeds scraped
1 teaspoon grated orange zest (optional)
2 tablespoons unsalted butter, at room temperature
white pepper in a mill
Preheat the oven to 350F. Put the potatoes on a baking sheet and bake in the oven until tender to a fork tip, about 1 hour. Remove from oven and let cook until warm enough to handle, 10 to 15 minutes. Peel and discard the skin. Put the potatoes in the bowl of a food processor fitted with the steel blade.
Meanwhile, pour the cream into a 2-quart pot, add the vanilla bean and orange zest, if using, and set it over medium heat. Bring to a simmer and cook for 5 minutes. Remove from heat. Use tongs to fish out and discard the vanilla bean. Pour the mixture over the potatoes in the processor and add the butter.
Puree the potato mixture until smooth. Season with salt and 4 grinds of pepper, or to taste. Keep covered and warm until ready to serve.