This potato and green bean coleslaw is a twist on a classic recipe.
Whisk together sugar, vinegar, sour cream, yogurt, 1 teaspoon salt, and pepper in a small bowl; set aside.
Bring a medium saucepan of water to a boil. Cut potatoes into long matchsticks (use a mandoline if you have one) and place in cold water to keep from discoloring. Drain sliced potatoes and add to boiling water along with 1 tablespoon salt. Cook until just tender, about 2 minutes. Remove potatoes with a slotted spoon and plunge into ice water. Keep cooking water at a boil. When potatoes are cold, drain and pat dry.
Add green beans to boiling water and cook until bright green and tender, about 3 minutes. Drain and plunge into ice water. When cold, drain and pat dry. Cut beans on the diagonal into 2-inch pieces; set aside.
Combine cabbage, potatoes, green beans, and sour-cream dressing in a large bowl; toss and adjust seasonings if necessary. Sprinkle with scallions, toss, and serve.