Preheat oven to 400 degrees. Rinse and scrub sweet potatoes, poke a few holes in each with a fork and rub each lightly with oil. Place on a large foil-lined baking sheet and bake until easily pierced through with a knife, about 45 min. Remove from oven and let cool until comfortable to handle. Peel off skins and slice flesh directly into the bowl of an electric mixer with the whisk attachment. Add remaining ingredients and whisk at medium speed, stopping to scrape down sides of bowl as necessary, until smooth. Transfer to a large baking dish and serve, or cover and place in a warm oven until ready to serve.
You can make this a day ahead and warm in a 300-degree oven until heated through when ready to serve.