Boil potatoes whole in their skins until tender about 15-20 minutes depending on their size. Drain and run under cold water. Once cool enough to handle rub off skins and cut into quarters or 1-inch cubes if using large potatoes.
While the potatoes are cooking, prepare the dressing. In a small bowl mix the lemon zest, white wine vinegar, and salt. Beat in the olive oil until well blended. The dressing should be a little sharp.
Toast cumin seeds in a heavy bottomed pan until they darken and you can smell their aroma. Do not let them burn. Immediately add them to the dressing. Mix well and let sit until the potatoes are ready.
Toss the prepared potatoes with the dressing. The potatoes should be slightly warm or at room temperature. Eat immediately, or for more flavor, cover and let sit at room temperature for at least 30 minutes.
When making a potato salad with vinaigrette dressing, always toss the salad together while the potatoes are still warm. They will then absorb the dressing, which in turn makes the salad more delicious.