2 pounds sweet potatoes, scrubbed
2 tart apples, such as Granny Smith or Braeburn
Juice of 1 lime
1/4 cup plain low-fat yogurt
1 to 2 tablespoons unsalted butter, melted (to taste)
1 tablespoon mild flavored honey, such as clover
Pinch of salt
Preheat the oven to 425 F. Scrub sweet potatoes and pierce in several places with a sharp knife. Pierce the apples in a few places. Line a baking sheet with foil and place the potatoes and apples on top. Bake for 40 minutes and remove the apples. Continue to bake the sweet potatoes until thoroughly soft and beginning to ooze, 5 to 15 minutes, depending on the size. Remove from the heat and allow to cool until cool enough to handle.
Turn the oven down to 350F. Remove the skins from the potatoes. Peel and core the apples, scraping all the flesh from just inside the skins. Chop the potatoes and apples coarsely and place in a food processor fitted with the steel blade. Puree until smooth. Add the remaining ingredients and blend well. Transfer to a lightly buttered 2- or 3-quart baking dish.
Heat the puree in the 350F oven for 20 to 30 minutes, until steaming. Serve hot.