Preheat oven to 400 degrees F.
Wrap each beet tightly in foil. [I usually like to double wrap mine in foil.] Drizzle the sweet potatoes with olive oil, and season with salt and pepper. Arrange the sweet potatoes in a singe layer on the baking sheet. Place the foil-wrapped beets on the same baking sheet. Roast for about 30 minutes, or until tender, but slightly crispy in the outside. Stir the sweet potatoes once or twice during roasting. [Watch the sweet potatoes closely, because they can go from perfectly roasted to imperfectly burnt.] Roast the beets for about an hour (or once you can poke a knife all the way through).
In a small mixing bowl, whisk together the shallots, lemon, olive oil, and truffle oil. Season with salt and pepper, to taste. Set aside.
Remove the sweet potatoes firstly from oven, followed by the beets when they have cooked through, and allow to cool just enough to be easily handled. Once cooled, peel “skin” off the beets. [They'll come off easily with just your hands -- no need for a paring knife.] Slice beets into 1 inch cubes.
In a large mixing bowl, combine the beets, sweet potatoes, and vinaigrette. Gently toss to combine all the ingredients. Divide onto small plates, sprinkle with chives, and drizzle with a little truffle oil, and enjoy!