2 sweet potato, peeled and cut into 3/4-inch cubes
2 potatoes, peeled and cut into 3/4 inch cubes
2 teaspoons distilled white vinegar
1/4 cup light mayonnaise
1/4 cup light sour cream
2 teaspoons fresh lemon juice
1 teaspoon curry powder, or to taste
salt and ground black pepper to taste
1/4 cup chopped green onions
1/2 cup chopped celery
1 tablespoon chopped fresh cilantro
Place potatoes in two separate saucepans and cover with water. Bring to a boil over high heat, then turn heat to medium-low. Cover, and cook until tender but still firm, 12 to 14 minutes for sweet potatoes, and 10 to 12 minutes for white potatoes. Drain and place in a large mixing bowl. Sprinkle with vinegar, and cool.
To make the dressing, combine the mayonnaise, sour cream, lemon juice, and curry powder in a small bowl. Season to taste with salt and pepper.
Mix the green onions, celery, and cilantro with the potatoes. Pour the dressing over the potato mixture, and toss to evenly coat vegetables. Refrigerate at least 1 hour before serving to let flavors blend.