(modified from Vegetarian Planet)
Place the russet potato pieces in a large saucepan, cover with water and bring to a boil. Then turn the heat down and simmer for about 10 minutes. Add the sweet-potato pieces and cook for another 15 minutes or so. Cook the potatoes to the point that they still have a little resistance to the tooth, not until they're falling to mush. Once the potatoes are tender, throw in the corn kernels and cook for 30 seconds. Remove immediately, drain, and leave them under cold running water or soaking in cold water to stop them from cooking any further.
In a large bowl combine the dressing ingredients; the Dijon mustard, lime juice, chopped cilantro, and garlic. Stir with a whisk and slowly pour in the oil while continuing to whisk. Season with salt and pepper.
Let the potato pieces drain and dice them into 1-inch cubes. Put the cubes, celery, and onion into the dressing and toss well. Serve chilled or room-temperature. Garnish with peanuts just before serving.