In a medium bowl, whisk together the olive oil, vinegar, mustard and 3/4 teaspoon each salt and pepper. Whisk in
the onion and chiles.
2. In a pot of salted water, bring the potatoes to a boil and cook until just tender, about 20 minutes. Drain, let cool, peel, then cut into bite-size pieces. Add to the vinaigrette.
3. Meanwhile, preheat the broiler. Broil the corn in the husks, turning, until charred on all sides. Let cool, then discard the husks and silk. Slice the kernels off the cobs. Add the kernels to the potatoes and vinaigrette; toss to combine.