Austrian-Style Potato Salad

1. Bring potatoes, broth, water, 1 teaspoon salt, sugar, and 1 tablespoon vinegar to boil in 12-inch skillet over high heat. Reduce heat to medium-low, cover, and cook until potatoes offer no resistance when pierced with paring knife, 15 to 17 minutes. Remove cover, increase heat to high (so cooking liquid will reduce), and cook 2 minutes.
2. Drain potatoes in colander set over large bowl, reserving cooking liquid. Set drained potatoes aside. Pour off and discard all but 1⁄2 cup cooking liquid (if 1⁄2 cup liquid does not remain, add water to make 1⁄2 cup). Whisk remaining tablespoon vinegar, mustard, and oil into cooking liquid.
3. Add 1⁄2 cup cooked potatoes to bowl with cooking liquid mixture and mash with potato masher or fork until thick sauce forms (mixture will be slightly chunky). Add remaining potatoes, onion, cornichons, and chives, folding gently with rubber spatula to combine. Season with salt and pepper to taste. Serve warm or at room temperature.

The finished salad should be creamy and loose, with chunks of potato that keep their shape but are very tender. If you can’t find cornichons, chopped kosher dill pickles can be substituted. For best results, don’t refrigerate the salad; it should be served within 4 hours of preparation.