3 lbs. red potatoes
1/3 cup lowfat sour cream
¼ cup mayonnaise
plain yogurt as needed
4-6 stalks scallions
salt and pepper

Put a pot of water on the stove and bring it to a boil. While you’re waiting, scrub the potatoes until they’re really clean (a vegetable scrub brush works well if you have one) – nobody likes a gritty texture in their potato salad. Dice up the potatoes into ¾"-or-so sized cubes. When the water’s boiling, dump in the potato cubes and cook for 20-25 minutes or so, until cooked through and tender. If you’re testing with a fork, try not to test the potatoes too frequently – the more holes you poke in them the more waterlogged they’ll get. Drain, rinse in cold water, and let cool. 

Meanwhile, make up the dressing. Chop the scallions and toss them in a large mixing bowl. Add the sour cream and mayonnaise and stir the mixture until well combined.. Toss the cooked cooled potatoes in the dressing, then add as much yogurt as needed to get it all good and coated (naturally, you can add either sour cream or mayonnaise if you prefer, which will give a stronger flavor but also, unfortunately, up the fat content). Sprinkle generously with salt and pepper to taste; refrigerate until ready to serve.